Skip to content

Heat and outdoor work: the rules that change a schedule

Heat is the one scheduling constraint where the law is actively moving, and it is moving differently in every country. In the past two years one country made heatstroke preparedness a criminal duty, one rewrote its rest framework around an instrument most rosters cannot yet read, one state added an indoor standard, one state forbade its own cities from writing heat rules, and the largest proposed standard of the lot is still a proposal.

This page holds every heat rule in the registry, 15 of them across 6 jurisdictions, and explains each one in the instrument it is actually written in. It does not put them in a column, because the moment you do that the page starts lying.

7 binding5 official guidance3 checked absencesevery source last read 6 August 2026

Read this before any figure below

Four jurisdictions, four thermometers, four different legal effects

The single most dangerous comparison in the set. Four different thermometers and four different legal effects, and the number 80 appears twice meaning unrelated things. California 80F is DRY-BULB air temperature triggering a shade duty (hard). US federal 80F is a HEAT INDEX triggering OSHA inspection attention and no employer duty at all (guidance). The proposed federal 80F is a heat index in a dormant rule. Japan WBGT 28C triggers a PREPAREDNESS duty (a named recipient of heatstroke reports and a written response procedure), not a break. Singapore WBGT 32C triggers a shaded REST BREAK. WBGT folds in humidity, radiant heat and air movement, so no fixed conversion to a dry-bulb or heat-index figure exists. Florida and the UK have no numeric trigger at all. Every heat rule now carries heatTriggerBasis; never render a heat figure without it.

A reader who lines up 28, 32, 80 and 95 in a single column has not learned something imprecise. They have learned something false. That is why this page is organised by jurisdiction and by instrument rather than by threshold.

The four instruments, each in its own terms

Every heat rule in the registry carries the basis its number is measured on, quoted below from the record rather than paraphrased. Two rules can share a figure and share nothing else.

Wet bulb globe temperature

As recorded, Singapore: WBGT (Wet Bulb Globe Temperature). Japan: WBGT 28C OR dry-bulb air temperature 31C, whichever is met first, measured in principle where the work is actually done.

WBGT is a composite of humidity, radiant heat and air movement as well as air temperature, which is the whole reason heat standards reach for it. A dry-bulb thermometer reports the same 80F on a dry morning and a saturated afternoon, but the body can shed heat by evaporation in the first case and cannot in the second, and direct sun on a paved surface adds a load the air reading never sees. Because WBGT folds in variables a thermometer ignores, no fixed offset converts one into the other. A site that knows its air temperature does not know its WBGT.

The operational consequence is a data dependency before it is a scheduling rule. Singapore requires a WBGT reading every 60 minutes through the working day, and sites above the S$5,000,000 contract sum, shipyards and the process industry cannot satisfy that with a public app reading. The reading is the switch that turns the rest cycle on, so a system that cannot ingest an hourly site-level measurement cannot implement the rule at all.

Dry-bulb air temperature

As recorded, California outdoor: outdoor dry-bulb air temperature in the work area. California indoor: indoor dry-bulb air temperature; the Tier 2 control-measures trigger is dry-bulb temperature OR heat index.

California measures the plain air temperature in the work area, which is the easiest instrument to read and the one most forecasts already provide. Its triggers do different jobs at different heights: shade maintained at all times above 80F outdoors, cool-down areas from 82F indoors with a further control tier at 87F, and high-heat procedures at 95F. The figures are legible to a scheduler precisely because they are ordinary temperatures, which is also why they get misquoted alongside numbers from other jurisdictions that only look similar.

Heat index

As recorded, federal inspection targeting: heat index (National Weather Service).

A heat index combines air temperature with relative humidity to express how hot conditions feel, and the National Weather Service publishes it. It sits between the other two instruments: more than a thermometer, less than WBGT, since it takes no account of radiant load or air movement. The federal 80F figure is a heat index, and it is the most dangerous number in the whole set to place in a table, because it is numerically identical to California's 80F dry-bulb shade trigger and legally unrelated to it. One obliges an employer to have shade. The other obliges nobody to do anything, and merely tells OSHA where to look.

No number at all

As recorded, United Kingdom: none: UK law states no maximum working temperature on any measurement basis. Federal general duty: none: the duty is outcome-based and states no threshold.

Three of the six jurisdictions regulate heat entirely through an outcome-based duty that names no threshold: the general duty clause in the federal United States and in Florida, and the risk assessment duty in the United Kingdom. All three are binding. An empty cell in this family means a binding duty with no number, never an absent obligation, and it is the reading of these rules that a comparison table gets most badly wrong. What a scheduler encodes here is not a threshold but a configurable employer trigger plus a record of which assessment it came from.

How to read the labels

Of the 15 heat records here, 7 are binding law, 5 are official but not binding, and 3 are checked absences where the finding is that no requirement exists. Those are three different answers and this page never blurs them.

Japan

Ministry of Health, Labour and Welfare (ๅŽš็”ŸๅŠดๅƒ็œ), Labour Standards Bureau, enforced locally by Prefectural Labour Bureaus and Labour Standards Inspection Offices (ๅŠดๅƒๅŸบๆบ–็›ฃ็ฃ็ฝฒ)

Japan is the clearest example of heat law moving from advice to obligation. Since 1 June 2025 the Ordinance on Industrial Safety and Health has carried a specific heatstroke article, and a breach is a criminal matter carrying up to 6 months of confinement or a fine of up to 500,000 yen. That is a stronger enforcement posture than anything else on this page.

What surprises people is what the duty actually asks for. It does not set a temperature at which work stops, and it does not buy anyone a break. It requires that before hot work starts there is a named way to report heatstroke symptoms and a written procedure for what happens next, both communicated to the people doing the work. The thresholds, WBGT 28C or air temperature 31C combined with 1 continuous hour or more than 4 hours in the day, come from the ministry's interpretive circular rather than the ordinance text, and both pairs are disjunctions. Breaking hot work into short stints does not escape the duty once the daily total passes 4 hours.

JapanHeat and outdoor work

Mandatory heatstroke reporting system and response procedure

Binding law

Before starting such work the employer must put in place, and inform the workers of, a system for reporting when a worker has heatstroke symptoms or when someone finds a colleague suspected of having heatstroke. The employer must also determine in advance, for each workplace, the content and implementation procedure for measures to stop symptoms worsening, covering removal from the work, cooling of the body and obtaining medical examination or treatment as needed, and must inform the workers of that content and procedure.

Who this covers

Applies to work at a 'hot place', meaning WBGT of 28C or above OR air temperature of 31C or above, where the work is expected to run continuously for 1 hour or more OR for more than 4 hoursโ€ฆRead the full scope

Applies to work at a 'hot place', meaning WBGT of 28C or above OR air temperature of 31C or above, where the work is expected to run continuously for 1 hour or more OR for more than 4 hours in the day. Both pairs are disjunctions, not conjunctions: WBGT 29 with air temperature 29 triggers the duty, and so does a day made of four separate 90-minute stints. Not limited to outdoor work: it covers indoor workplaces, work at customer or travel sites, work across multiple locations and travel between them, and the temperature is measured in principle at the place the work is actually done. The duty covers all persons doing the work at the site, including non-employees, and on mixed sites it falls on the principal contractor and every subcontractor independently.

When it triggers: (wbgtAtLeastC OR airTempAtLeastC) AND (continuousHoursAtLeast OR dailyHoursOver)

How to encode this in a schedule

Rosters a role, not a rest break. Whenever a block meets the temperature and duration trigger, the scheduler must ensure a named recipient of heatstroke reports is on duty and contactable for the entire block, and must not schedule such work at a site whose response procedure has not been recorded and communicated. Because the trigger is 'continuously 1 hour or more OR more than 4 hours a day', splitting the work into short stints does not avoid it once the daily total passes 4 hours.

WBGT celsius
28
Heat trigger C
31
Continuous hours at least
1
Daily hours over
4
Penalty months imprisonment
6
Penalty max fine yen
500,000
Heat trigger basis:
WBGT 28C OR dry-bulb air temperature 31C, whichever is met first, measured in principle where the work is actually done

The mistake employers make

The numbers are not in the ordinance. Article 612-2 says only 'work carried out continuously in a hot place and other work liable to cause heatstroke'; the WBGT 28C, 31C, 1-hour and 4-hour figures come from the ministry's interpretive circular, which is what inspectors apply. Two further misreadings are common: this is not an outdoor-only rule, and it does not require a rest break or a work-stoppage temperature. What it mandates is that someone is designated to receive reports and that a written response procedure exists and has been communicated before the work starts. Breach carries up to 6 months confinement or a fine up to 500,000 yen.

Why this figure does not travel

wbgtCelsius 28 triggers a PREPAREDNESS duty (a named recipient for heatstroke reports and a written response procedure). Singapore's wbgtCelsius 32 triggers a paid shaded REST BREAK. These are not points on the same scale and must never be rendered as 'Japan is stricter than Singapore'.

Why this label and not another

Kept as 'hard': Article 612-2 of the Ordinance on Industrial Safety and Health is a specific, criminally enforceable duty. Only the THRESHOLDS (WBGT 28C, 31C air, 1 hour, 4 hours) come from the ministry's interpretive circular rather than the ordinance text. That is why this rule is 'hard' while the Singapore heat framework, whose entire content including the duty itself sits in an administrative document under a general duty clause, is 'guidance'.

Citation: Ordinance on Industrial Safety and Health (Ministry of Labour Ordinance No. 32 of 1972) Article 612-2, added by MHLW Ordinance No. 57 of 2025; based on Industrial Safety and Health Act Article 22; penalties under Industrial Safety and Health Act Article 119(i)

Ministry of Health, Labour and Welfare, Labour Standards Bureau Circular Kihatsu 0520 No. 6 of 20 May 2025 (official interpretive circular on the amending ordinance)last read 6 August 2026

In force from 1 June 2025

Singapore

Ministry of Manpower (MOM)

Singapore has the most detailed heat framework in the set and the most awkward label. The Ministry of Manpower calls its measures required, distinguishes them from the recommended practices printed alongside them, inspects against them, and can respond to non-implementation with stop-work orders and composition fines. Read that and you would call it binding.

The reason this engine records it as official guidance is narrow and specific: the figures have no legislative source. The 32C and 10-minute pairing does not appear in any Act or subsidiary legislation. It sits in a framework document, and the binding instrument behind it is a general duty in the Workplace Safety and Health Act that contains no numbers at all. The label describes where the numbers come from, not how much enforcement exposure they carry, and it understates that exposure. A scheduler in Singapore should build to these figures exactly as if they were statutory, then read the trap note below to understand why the two are not the same claim.

SingaporeHeat and outdoor work

Hourly shaded rest breaks for heavy outdoor work above WBGT 32C

Official guidance

MOM's heat stress framework for outdoor work requires, as a stated required measure, hourly rest breaks of at least 10 minutes for heavy physical work activity once WBGT reaches 32C, rising to at least 15 minutes once WBGT reaches 33C, with longer rest periods recommended as WBGT increases further. Below 32C the requirement is adequate rest under shade for recovery from heat, with rest areas near work areas where feasible. Workers must be able to rehydrate at least hourly from a cool or cold water supply near the work area at WBGT 31C and above, with a recommended intake of 300ml per hour or more depending on work intensity.

Who this covers

Outdoor workers doing heavy physical work activity, at any salary and in any role. Independent of Part 4 of the Employment Act, so it reaches managers, executives and employees above theโ€ฆRead the full scope

Outdoor workers doing heavy physical work activity, at any salary and in any role. Independent of Part 4 of the Employment Act, so it reaches managers, executives and employees above the salary caps. The framework's rest requirement is expressed for heavy physical work activity; the framework does not define heavy numerically.

How to encode this in a schedule

Weather-reactive intraday constraint rather than a roster-build constraint: for outdoor heavy-work assignments, ingest hourly WBGT and insert a non-working shaded interval of at least 10 minutes into each clock hour once WBGT >= 32, and at least 15 minutes once WBGT >= 33, plus an hourly hydration point from WBGT >= 31. Because the trigger is measured on the day, the schedule must carry enough coverage slack to absorb roughly 17 to 25 percent of on-site hours being non-productive on hot days, and the intraday engine, not the weekly roster, must own the insertion.

Break minutes
10
Break minutes tier 2
15
WBGT celsius hydration
31
WBGT celsius tier 2
33
Recommended hydration mL per hour
300
WBGT celsius
32
After hours
1
After hours tier 2
1
Heat trigger basis:
WBGT (Wet Bulb Globe Temperature)

The mistake employers make

The status of these numbers is the thing people get wrong in both directions. MOM labels them required measures that must be implemented, distinguishes them explicitly from the recommended practices in the same document, and inspects against them, and non-implementation can attract stop-work orders and composition fines under the Workplace Safety and Health Act. But the 32C/10-minute and 33C/15-minute figures do not appear in any Act or subsidiary legislation; they sit in a MOM framework document, and the binding instrument behind them is the general duty in section 12 of the Workplace Safety and Health Act to take, so far as is reasonably practicable, such measures as are necessary to ensure employees' safety and health, which contains no numbers at all. Treating them as advisory understates the enforcement exposure; treating them as a statutory rest-break entitlement of the same kind as the Employment Act's 45 minutes misstates the law. This file records them as guidance because the numbers have no legislative source, not because compliance is optional.

Why this figure does not travel

wbgtCelsius 32 is not convertible to California's 80F/95F dry-bulb triggers or to the federal heat-index triggers: WBGT folds in humidity, radiant heat and air movement, so no fixed offset exists. breakMinutes 10 / afterHours 1 is also twice the cadence of California's mandatory agricultural 10-per-2-hours, while carrying less legal force.

Citation: MOM Heat Stress Measures for Outdoor Work (revised framework published with MOM press release of 6 September 2024); enforced under the general duty of employers in the Workplace Safety and Health Act 2006, section 12

Ministry of Manpowerlast read 6 August 2026

In force from 6 September 2024

SingaporeHeat and outdoor work

Seven-day graduated acclimatisation for new and returning outdoor workers

Official guidance

Employers must acclimatise workers who are new to Singapore or returning from leave of more than a week by gradually increasing their daily heat exposure over at least 7 days. This is listed as a required measure in every WBGT band of MOM's framework, including the lowest. The framework does not prescribe a percentage ramp for each day.

Who this covers

Outdoor workers new to Singapore, and outdoor workers returning from leave of more than one week. Applies at every WBGT band, including below 31C. Independent of Employment Act Part 4 salary caps.

How to encode this in a schedule

Per-worker ramp state rather than a per-shift check: on hire, on first arrival in Singapore, and on return from any absence longer than 7 days, open a 7-day acclimatisation window in which the worker's daily outdoor heat exposure increases progressively. The scheduler needs a graduated-exposure capacity per day rather than a binary available/unavailable flag, and needs to re-open the window automatically on return from long leave, which is the case teams forget.

Acclimatisation days
7
Returning from leave days trigger
7

The mistake employers make

Acclimatisation is usually implemented once, at onboarding, and then never again. The framework's trigger is also 'returning from leave of more than a week', which means a long-serving worker back from a two-week home visit needs a fresh 7-day ramp. The same worker is separately on MOM's vulnerable-worker list while unacclimatised, which at WBGT 33C and above turns into a required redeployment to non-outdoor work.

Why this figure does not travel

The only live acclimatisation duty in this set. The federal U.S. equivalent (us-federal-heat-proposed-standard) is dormant and specifies a percentage ramp; Singapore's specifies a 7-day period with no ramp figures. Do not fill Singapore's missing percentages from the U.S. proposal.

Citation: MOM Heat Stress Measures for Outdoor Work (revised framework, Annex to MOM press release of 6 September 2024); enforced under the general duties in the Workplace Safety and Health Act 2006, section 12

Ministry of Manpowerlast read 6 August 2026

In force from 6 September 2024

SingaporeHeat and outdoor work

WBGT must be monitored every hour during work hours

Official guidance

Employers must monitor the Wet Bulb Globe Temperature every hour during work hours, especially during the hotter parts of the day. Construction sites with a contract sum of S$5 million or more, shipyards and the process industry must use on-site WBGT meters rather than a public reading.

Who this covers

All outdoor work, at every WBGT band. On-site WBGT meters are required for construction sites with a contract sum of S$5 million or more, for shipyards and for the process industry; other workplaces may use the National Environment Agency's myENV app.

How to encode this in a schedule

Recurring assigned task plus a data dependency: every outdoor site needs a named owner for an hourly WBGT reading across the whole span of outdoor work, and the reading is the input that switches the rest-cycle constraint on and off. A scheduler that cannot ingest an hourly site-level environmental reading cannot implement the rest-cycle rule at all, so this is the integration point rather than a nice-to-have.

WBGT monitoring interval minutes
60
On site meter contract sum threshold SGD
5,000,000
Heat trigger basis:
WBGT (Wet Bulb Globe Temperature)

The mistake employers make

Large construction sites, shipyards and process-industry sites cannot satisfy this with the myENV app reading. They need an on-site meter, and the S$5 million trigger is the contract sum, not headcount or site area, so a small crew on a large contract is still in scope. The on-site meter obligation is also older than the current framework: it was announced with the October 2023 measures and took effect on 1 January 2024, so a site cannot treat September 2024 as the start of its meter duty.

Citation: MOM Heat Stress Measures for Outdoor Work (revised framework published with MOM press release of 6 September 2024), 'Monitor WBGT' required measure, applicable in every WBGT band; enforced under the general duty of employers in the Workplace Safety and Health Act 2006, section 12

Ministry of Manpowerlast read 6 August 2026

In force from 6 September 2024

California

California Department of Industrial Relations (wage and hour rules enforced by the Division of Labor Standards Enforcement, known as the Labor Commissioner's Office; heat illness standards enforced by the Division of Occupational Safety and Health, Cal/OSHA)

California is where heat becomes arithmetic. It is the only jurisdiction here with numeric triggers that a roster can be built against directly, and it now has two standards rather than one: the long-standing outdoor standard and an indoor standard that has been operative since 23 July 2024.

The indoor standard is the one that catches people. A 82F work area is an ordinary summer afternoon in an un-airconditioned kitchen, a retail back room or a stockroom, and those are precisely the places a scheduler assumes no heat rule reaches. The outdoor standard, meanwhile, mostly produces capacity pressure rather than fixed break slots: cool-down rests are employee-initiated and unbounded in number, so what an outdoor roster needs above 80F is slack, not a scheduled interval. The one fixed, schedulable cadence in California is agricultural, and it is buried inside a subsection about high-heat procedures rather than in the break rules.

CaliforniaHeat and outdoor work

Outdoor shade at 80F and cool-down rest on demand

Binding law

When the outdoor temperature in the work area exceeds 80F, the employer shall have and maintain one or more areas with shade at all times while employees are present, either open to the air or provided with ventilation or cooling, enough to accommodate the number of employees on recovery or rest periods so they can sit in a normal posture fully in the shade without physical contact with each other, located as close as practicable to the areas where employees are working. When the outdoor temperature does not exceed 80F the employer shall either provide that shade or provide timely access to shade upon an employee's request. Employees shall be allowed and encouraged to take a preventative cool-down rest in the shade when they feel the need to do so to protect themselves from overheating, and such access to shade shall be permitted at all times. An employee taking a preventative cool-down rest shall be monitored, asked if experiencing symptoms of heat illness, encouraged to remain in the shade, and shall not be ordered back to work until any signs or symptoms of heat illness have abated, but in no event less than 5 minutes in addition to the time needed to access the shade.

Who this covers

8 CCR 3395 applies to all outdoor places of employment. The cool-down rest entitlement in subsection (d)(3) applies at all times, not only above 80F. Two exceptions to the shade duty: whereโ€ฆRead the full scope

8 CCR 3395 applies to all outdoor places of employment. The cool-down rest entitlement in subsection (d)(3) applies at all times, not only above 80F. Two exceptions to the shade duty: where the employer can demonstrate it is infeasible or unsafe to have a shade structure it may use alternative procedures giving equivalent protection, and except in agriculture, cooling measures other than shade may be substituted where demonstrably at least as effective.

How to encode this in a schedule

Soft-capacity constraint rather than a fixed break: cool-down rests are employee-initiated and unbounded in number, so on days forecast above 80F an outdoor roster needs slack built into required coverage rather than a scheduled break slot. On the reading that a preventative cool-down rest is a recovery period within Labor Code 226.7, denying one costs an hour of premium pay for that workday; that consequence is inferred from 226.7(a) and (c) rather than stated in 3395, so treat it as likely rather than certain when costing.

Heat trigger F
80
Minimum cool down rest minutes
5
Cool down rest excludes travel to shade
yes
Cool down rest is paid
yes
Heat trigger C
26.7
Paid status derivation:
Derived, not quoted: 8 CCR 3395 does not itself say 'paid'. Labor Code 226.7(a) defines a 'recovery period' as 'a cooldown period afforded an employee to prevent heat illness', and 226.7(d) provides that a rest or recovery period mandated pursuant to state law shall be counted as hours worked with no deduction from wages. A preventative cool-down rest under 3395(d)(3) fits that definition.
Heat trigger basis:
outdoor dry-bulb air temperature in the work area

The mistake employers make

The five-minute minimum is a floor, not the entitlement, and it excludes walking time to the shade. The rest continues until symptoms abate, so a scheduler who budgets exactly five minutes of relief per employee has under-planned. Employers also treat 80F as the trigger for the whole standard, but access to shade on request and the right to a cool-down rest exist at any temperature.

Why this figure does not travel

heatTriggerF 80 is a DRY-BULB AIR TEMPERATURE and triggers a shade duty, not a break. It is numerically equal to the federal NEP inspection trigger (a heat index) and to the proposed federal standard's initial trigger (a heat index), and legally unlike both. minimumCoolDownRestMinutes 5 is a floor on an employee-initiated rest of unbounded frequency, not a scheduled cadence, so it does not compare with breakMinutes anywhere.

Citation: 8 CCR section 3395(a)(1), (d)(1)-(3); California Labor Code section 226.7(a), (c) and (d) for the paid and premium consequences

California Department of Industrial Relations, California Code of Regulations Title 8 section 3395last read 6 August 2026

CaliforniaHeat and outdoor work

High-heat procedures at 95F, with mandatory timed cool-down rests in agriculture

Binding law

The employer shall implement high-heat procedures when the temperature equals or exceeds 95F. These procedures shall include, to the extent practicable: effective communication by voice, observation or electronic means so employees can contact a supervisor when necessary; observing employees for alertness and signs or symptoms of heat illness through supervisor or designee observation of 20 or fewer employees, a mandatory buddy system, regular communication with a sole employee, or other effective means; designating one or more employees on each worksite as authorised to call for emergency medical services; reminding employees throughout the shift to drink plenty of water; and pre-shift meetings to review the high heat procedures. For employees employed in agriculture, when temperatures reach 95F or above the employer shall ensure that the employee takes a minimum ten minute net preventative cool-down rest period every two hours.

Who this covers

8 CCR 3395(a)(1) states that if an industry is not listed in subsection (a)(2), employers in that industry are not required to comply with subsection (e). The listed industries areโ€ฆRead the full scope

8 CCR 3395(a)(1) states that if an industry is not listed in subsection (a)(2), employers in that industry are not required to comply with subsection (e). The listed industries are agriculture, construction, landscaping, oil and gas extraction, and transportation or delivery of agricultural products, construction materials or other heavy materials (for example furniture, lumber, freight, cargo, cabinets, industrial or commercial materials), EXCEPT for employment that consists of operating an air-conditioned vehicle and does not include loading or unloading. The mandatory timed cool-down rest in subsection (e)(6) applies only to employees employed in agriculture.

How to encode this in a schedule

Hard constraint for agriculture on days at or above 95F: every assignment block must contain a 10-minute net non-working interval every two hours. The regulation permits these to be provided concurrently with any other meal or rest period required by IWC Order No. 14 where the timing coincides, so an eight-hour day may need no additional interval, but a day extending past eight hours requires an extra cool-down at the conclusion of the eighth hour, another at the conclusion of the tenth, and so on. For the other four listed industries the effect is a supervision constraint: at least one observer per 20 or fewer employees, or a buddy system, must be rostered.

Heat trigger F
95
Break minutes
10
After hours
2
Supervisor observation ratio max
20
Additional rest at end of hour
8, 10
Heat trigger C
35
Break applies to sectors
agriculture
Additional rest at end of hour note:
The regulation says a further cool-down rest is required at the conclusion of the eighth hour if the workday extends beyond eight hours, another at the conclusion of the tenth hour if it extends beyond ten, 'and so on', so the list continues past 10 for longer days.
Heat trigger basis:
outdoor dry-bulb air temperature in the work area

The mistake employers make

The agricultural cool-down cadence is the only heat rule in California that produces a fixed, schedulable break, and it is the one most often missed because it is buried in a subsection about high-heat procedures rather than in the break provisions. The escalation past eight hours is missed more often still: a ten-hour picking day at 96F requires cool-down rests at the eighth and tenth hours on top of the wage order breaks. The delivery carve-out cuts the other way and is also missed: a driver operating an air-conditioned vehicle who never loads or unloads is outside subsection (e) entirely.

Why this figure does not travel

breakMinutes 10 / afterHours 2 is MANDATORY but only for agriculture, and only at or above 95F dry-bulb. Singapore's breakMinutes 10 / afterHours 1 is guidance, applies to any heavy outdoor work at WBGT 32C, and is measured per clock hour. The proposed federal 15/2 is dormant. Three superficially similar cadences with different legal force, different sectors and different thermometers.

Citation: 8 CCR section 3395(a)(1)-(2) and (e), including (e)(6)

California Department of Industrial Relations, California Code of Regulations Title 8 section 3395last read 6 August 2026

CaliforniaHeat and outdoor work

Indoor heat standard: cool-down area access from 82F

Binding law

Where an indoor work area reaches 82F, the employer shall have and maintain one or more cool-down areas, whose temperature shall be maintained at less than 82F unless the employer demonstrates it is infeasible, large enough to accommodate the number of employees on recovery or rest periods in a normal posture without physical contact, located as close as practicable to where employees are working. Employees shall be allowed and encouraged to take a preventative cool-down rest in a cool-down area when they feel the need to do so, at all times, and shall not be ordered back to work until any signs or symptoms of heat illness have abated, and in no event less than five minutes in addition to the time needed to access the cool-down area.

Who this covers

This is the INDOOR standard, 8 CCR section 3396, distinct from the outdoor standard above. It applies to all indoor work areas where the temperature equals or exceeds 82F when employees areโ€ฆRead the full scope

This is the INDOOR standard, 8 CCR section 3396, distinct from the outdoor standard above. It applies to all indoor work areas where the temperature equals or exceeds 82F when employees are present. Exceptions read verbatim from subsection (a)(1): it does not apply where employees are teleworking from a location of the employee's choice not under the employer's control; it does not apply to incidental heat exposures where an employee is exposed at or above 82F and below 95F for less than 15 minutes in any 60-minute period, and that incidental exception does not apply to vehicles without effective and functioning air conditioning or to shipping or intermodal containers during loading, unloading or related work; it does not apply to emergency operations directly involved in the protection of life or property; and it exempts state prisons under Penal Code 6082, local detention facilities under Penal Code 6031.4, and juvenile facilities under Welfare and Institutions Code 850 and 875(g) operated by a local government. The additional control measures in subsection (e) apply only where the temperature or heat index equals or exceeds 87F, or where the temperature equals or exceeds 82F and employees wear clothing that restricts heat removal or work in a high radiant heat area.

How to encode this in a schedule

Same shape as the outdoor cool-down rule and applies to indoor retail stockrooms, warehouses, commercial kitchens and laundries, which is where schedulers most often assume no heat rule exists. On days a site is expected to reach 82F indoors, plan slack in required coverage for employee-initiated cool-down rests. As with the outdoor standard, the paid status and the one-hour premium for denial are inferred from Labor Code 226.7(a), (c) and (d) rather than stated in 3396.

Heat trigger F
82
Heat trigger tier 2 F
87
Control measures trigger heat index F
87
Control measures trigger frestrictive clothing or radiant heat
82
Cool down area max temp F
82
Minimum cool down rest minutes
5
Incidental exposure exemption minutes per 60
15
Incidental exposure exemption upper bound F
95
Heat trigger C
27.8
Heat trigger tier 2 C
30.6
Heat trigger basis:
indoor dry-bulb air temperature; the Tier 2 control-measures trigger is dry-bulb temperature OR heat index

The mistake employers make

This standard is recent and is widely assumed to be an agriculture or warehouse rule. It is not: 82F is an ordinary summer afternoon in an un-airconditioned restaurant kitchen or a retail back room, and the standard applies to those work areas by its own terms. The 15-minute incidental exposure exemption does not rescue a delivery driver in a vehicle without working air conditioning, nor anyone loading or unloading a shipping container.

Why this figure does not travel

This is the INDOOR standard (8 CCR 3396) filed under heat-outdoor because the canonical topic list has no heat-indoor value. Japan's heat rule is likewise indoor and outdoor. Any 'outdoor heat' comparison built from the topic alone will silently include indoor rules.

Citation: 8 CCR section 3396(a), (b) and (d); California Labor Code section 226.7(a), (c) and (d) for the paid and premium consequences

California Department of Industrial Relations, California Code of Regulations Title 8 section 3396last read 6 August 2026

In force from 23 July 2024

United States (federal)

U.S. Department of Labor, Wage and Hour Division (Fair Labor Standards Act); Occupational Safety and Health Administration (OSH Act)

The federal picture is the one employers get wrong most often, in both directions. There is no federal heat standard in force. The proposed rule published in August 2024 remains a proposal, and as of the verification date on these records no final rule has issued. Anyone quoting the 80F and 90F triggers or the 15-minute break as a current federal requirement is quoting a document with no legal force.

That is not the same as saying heat is unregulated federally. The general duty clause is binding, OSHA cites heat under it, and the National Emphasis Program reissued in April 2026 targets inspections across 55 industries for up to 5 years. The awkward part for a scheduler is that the binding rule has no number and the rule with numbers is not binding. Encode the duty as a requirement that a heat plan exists and is applied, and treat the 80F heat index figure as a flag on the day rather than a rule on the shift.

United States (federal)Heat and outdoor work

General Duty Clause obligation to control recognized heat hazards

Binding law

Each employer shall furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees. OSHA uses this provision to cite heat hazards, but it specifies no temperature threshold, no rest schedule and no shade or water requirement.

Who this covers

Applies to indoor and outdoor work alike; the previous 'outdoor: true' flag contradicted this rule's own scope and has been cleared. Covers employers with employees under OSH Actโ€ฆRead the full scope

Applies to indoor and outdoor work alike; the previous 'outdoor: true' flag contradicted this rule's own scope and has been cleared. Covers employers with employees under OSH Act jurisdiction. It does not reach the self-employed, does not reach state and local government employees except in states with an OSHA-approved State Plan, and does not reach workplaces regulated under another federal agency's occupational safety authority. There is no federal heat standard, so heat is cited under the general duty provision. A number of State Plan states have adopted specific heat standards that impose concrete numeric duties the federal layer does not; those must be read from the relevant state jurisdiction rather than assumed from this federal entry.

How to encode this in a schedule

Binding but numerically empty, so it cannot be encoded as a threshold. It is best modelled as a requirement that a heat control plan exists and is applied when conditions warrant, with the actual triggers drawn from the applicable State Plan standard or from the employer's own policy. A scheduler should surface it as a duty to act rather than as a computable constraint.

Heat trigger basis:
none: the duty is outcome-based and states no threshold

The mistake employers make

Employers read the absence of a federal heat standard as the absence of a federal heat obligation. OSHA has issued General Duty Clause citations and Hazard Alert Letters for heat, and the revised National Emphasis Program builds its target industry list partly from that citation and hazard-alert-letter history. The clause is genuinely binding; it simply gives the employer no numbers to comply with.

Why this figure does not travel

Binding but numberless. Sits in the same family as uk-heat-outdoor-risk-assessment-duty and us-florida-heat-outdoor-osha-general-duty: a hard duty with no encodable trigger. Never render it in a column against California's 80F or Singapore's WBGT 32C as though the absence of a number meant the absence of a duty.

Citation: Occupational Safety and Health Act of 1970, section 5(a)(1), 29 U.S.C. 654(a)(1)

U.S. Government Publishing Office, govinfo (United States Code, 2024 edition)last read 6 August 2026

United States (federal)Heat and outdoor work

Heat National Emphasis Program inspection targeting at 80F heat index

Official guidance

OSHA's National Emphasis Program for outdoor and indoor heat-related hazards directs enforcement attention through two distinct triggers, which are easily conflated. First, programmed inspections drawn from the Appendix A target industry lists shall occur on any day that the National Weather Service has announced a heat warning or advisory for the local area. Second, a heat priority day occurs when the heat index for the day is expected to be 80 degrees Fahrenheit or more; on such days the Area Office will assess the potential for serious heat-related illnesses and injuries, and compliance officers conducting inspections opened for other purposes should inquire about the existence of any heat-related hazard prevention programs. Compliance officers investigating for other purposes must also expand or refer a heat inspection wherever there is evidence of violative conditions. Enforcement rests on the General Duty Clause, 29 U.S.C. 654.

Who this covers

The directive states that it applies OSHA-wide, covering general industry, construction, maritime and agriculture, in both indoor and outdoor settings; the previous 'outdoor: true' flag contradicted that and has been cleared. It directs OSHA's own inspectors; it creates no new duty on any employer.

How to encode this in a schedule

Not an employer obligation, so it must not be encoded as a schedule constraint. Its practical use is as a risk signal: on forecast days where the heat index reaches 80F, an employer in a targeted industry faces materially elevated inspection probability, and on days carrying an NWS heat warning or advisory it faces the programmed-inspection list directly. Treat it as a flag on the day, not a rule on the shift.

Heat trigger F
80
Heat trigger C
26.7
Targeted industry count
55
Targeted industries added
22
Targeted industries removed
46
Targeted industries retained
33
Duration years
5
Heat trigger basis:
heat index (National Weather Service)

The mistake employers make

The 80F heat index figure is widely quoted as though it were a regulatory threshold that obliges employers to provide breaks or shade. It is not. It is a trigger for OSHA attention. The second and subtler trap is assuming 80F is what puts an establishment on the programmed inspection list; that is driven by NWS heat warnings and advisories together with the Appendix A industry list. The revised directive also lists a revised inspection goal among its significant changes and states no numerical inspection quota, so the program is targeted by industry list rather than by inspection count.

Why this figure does not travel

heatTriggerF 80 triggers OSHA INSPECTION ATTENTION, not any employer duty. It is numerically identical to California's 80F shade trigger and to the proposed federal standard's initial trigger, and legally unrelated to both. This is the most dangerous number in the whole set to place in a comparison table.

Citation: OSHA Instruction CPL 03-00-024, National Emphasis Program, Outdoor and Indoor Heat-Related Hazards, 10 April 2026, sections VII (Expiration), XII.C (Inspection Scheduling), XII.D.1 and Appendix A

Occupational Safety and Health Administrationlast read 6 August 2026

In force from 10 April 2026

United States (federal)Heat and outdoor work

Proposed federal heat standard, not in effect

Official guidance

This is a proposed rule only and is not in force. As proposed, it would set an initial heat trigger at a heat index of 80F or a wet bulb globe temperature equal to the NIOSH Recommended Alert Limit, and a high heat trigger at a heat index of 90F or a WBGT equal to the NIOSH Recommended Exposure Limit. At or above the high heat trigger the employer would have to provide a minimum 15-minute paid rest break at least every two hours. For acclimatisation the employer would choose between two alternative protocols rather than being required to ramp: either applying the high-heat-trigger controls of paragraph (f) throughout the employee's first week whenever the heat index is at or above the initial heat trigger, or gradually restricting heat exposure to no more than 20 percent of a normal work shift on day one, 40 percent on day two, 60 percent on day three and 80 percent on day four. The same choice applies to employees returning after more than 14 days away, whose gradual option is 50 percent, then 60 percent, then 80 percent.

Who this covers

If finalised, would apply to all employers conducting outdoor and indoor work in general industry, construction, maritime and agriculture where OSHA has jurisdiction, as proposed 29 CFRโ€ฆRead the full scope

If finalised, would apply to all employers conducting outdoor and indoor work in general industry, construction, maritime and agriculture where OSHA has jurisdiction, as proposed 29 CFR 1910.148 with parallel amendments to parts 1915, 1917, 1918, 1926 and 1928. Proposed 1910.148(a)(2) would exclude work activities with no reasonable expectation of exposure at or above the initial heat trigger; short-duration exposures at or above that trigger of 15 minutes or less in any 60-minute period; organisations whose primary function is firefighting and specified emergency response activities; work in indoor areas or vehicles where air-conditioning consistently keeps the ambient temperature below 80F; and telework. As of the verification date it imposes no obligation on any employer.

How to encode this in a schedule

Must not be enforced as a constraint today. Worth modelling as a dormant rule set so that employers can see the shape of the coming obligation: a 15-minute paid break every 2 hours above a 90F heat index would materially change summer outdoor rosters, and the gradual acclimatisation option would cap a new hire's first-week shift lengths at a fraction of normal. Model the acclimatisation ramp as one branch of an employer election, not as a mandatory ramp. Keep the whole rule set disabled until and unless a final rule issues.

Heat trigger F
80
Heat trigger C
26.7
Heat trigger tier 2 F
90
Heat trigger tier 2 C
32.2
Break minutes
15
After hours
2
Short duration exclusion minutes per 60
15
Acclimatization is one of two options
yes
Acclimatization day 1 percent
20
Acclimatization day 2 percent
40
Acclimatization day 3 percent
60
Acclimatization day 4 percent
80
Returning worker day 1 percent
50
Returning worker day 2 percent
60
Returning worker day 3 percent
80
Returning worker absence days exceeding
14
Heat trigger basis:
heat index, or WBGT measured against the NIOSH Recommended Alert Limit (initial) and Recommended Exposure Limit (high heat)

The mistake employers make

Vendors and employers have begun citing the 80F and 90F triggers and the 15-minute break as current federal requirements. They are not. The only binding federal heat obligation remains the General Duty Clause. A second trap for anyone pre-building the rule set is treating the acclimatisation percentages as the standard's mandate; they are one of two protocols the employer may choose.

Why this figure does not travel

breakMinutes 15 / afterHours 2 is a PROPOSED cadence with no force. It sits in the same key shape as California's mandatory agricultural 10-minutes-every-2-hours and Singapore's 10-minutes-every-1-hour, and must be rendered as dormant wherever those are rendered as live.

Citation: Heat Injury and Illness Prevention in Outdoor and Indoor Work Settings, Notice of Proposed Rulemaking, 89 FR 70698 (30 August 2024), Docket No. OSHA-2021-0009, proposed 29 CFR 1910.148(a)(2), (e)(7) and (f)(2)

Occupational Safety and Health Administrationlast read 6 August 2026

Florida

Florida Department of Business and Professional Regulation (Fla. Stat. 450.012(4) defines 'department' as DBPR; 450.121(1) makes it the administrator of the Child Labor Law), whose scheduling jurisdiction is limited to the Child Labor Law. Adult scheduling has no general state enforcer; the U.S. Department of Labor Wage and Hour Division and federal OSHA cover the remainder, and the Florida Department of Highway Safety and Motor Vehicles / Florida Highway Patrol enforce the commercial motor vehicle hours rules adopted by Fla. Stat. 316.302.

Florida is the only place on this page where the absence of a heat rule was legislated rather than merely left alone. Since 1 July 2024 a Florida county or city may not require an employer to provide heat exposure measures beyond state or federal law, and the statute spells out what that covers: monitoring, water, cooling measures, acclimation and recovery periods, training, notices and recordkeeping.

Florida has no state heat standard and no OSHA-approved State Plan, so beyond state or federal law resolves to the general duty clause, which attaches no number to anything. The result for a private employer is that no cool-down interval is mandated anywhere in the state, and any recovery pattern in the roster is employer policy rather than a jurisdiction rule. Two carve-outs matter operationally. A political subdivision may still set heat rules for its own direct workforce, and Florida state and local government employees are outside federal OSHA coverage entirely, so a city road crew and a private crew working the same street in July are on different footings.

FloridaHeat and outdoor work

Local heat exposure requirements preempted, including recovery periods

No requirement

Since 1 July 2024, a Florida political subdivision may not establish, mandate, or otherwise require an employer to meet or provide heat exposure requirements not otherwise required under state or federal law. The statute defines heat exposure requirements to include employee monitoring and protection, water consumption, cooling measures, acclimation and recovery periods or practices, posting or distributing notices, heat exposure programs or training, first aid and emergency responses, protections for employees who report excessive heat exposure, and reporting and recordkeeping. A political subdivision may also not give preference in a competitive solicitation based on an employer's heat exposure requirements, and may not consider or seek information relating to them. Florida itself has no heat standard.

Who this covers

All employers in Florida, including employers contracting to provide goods or services to a political subdivision. 'Political subdivision' is defined broadly as a county, municipalityโ€ฆRead the full scope

All employers in Florida, including employers contracting to provide goods or services to a political subdivision. 'Political subdivision' is defined broadly as a county, municipality, department, commission, district, board, or other public body created by or under state law. Two carve-outs: a political subdivision may still set heat exposure requirements for its own direct employees (s. 448.106(3)), and the section does not apply to the extent necessary where compliance would prevent distribution of federal funds or be inconsistent with federal funding requirements (s. 448.106(4)).

How to encode this in a schedule

There is no legally mandated cool-down or recovery interval to encode for private employers anywhere in Florida. Heat recovery breaks are an employer policy parameter, not a jurisdiction rule. The one place a local rule can still bind is a political subdivision scheduling its own direct workforce, so heat break configuration belongs at the organisation level rather than being keyed to the Florida jurisdiction.

Heat trigger basis:
none: no Florida heat standard exists and none may be created locally

The mistake employers make

Reading preemption as an exemption. Federal OSHA's general duty clause still applies to private employers in Florida and is enforced case by case with no number attached, so scheduling a 10-hour July roofing shift with no recovery breaks remains exposed to a general duty citation even though no Florida ordinance may require one.

Why this label and not another

Downgraded from 'hard' for the same reason as us-florida-predictive-scheduling-local-preemption. Fla. Stat. 448.106 is binding on political subdivisions and imposes no duty on any employer. The scheduling-facing claim is an absence: no heat recovery interval is mandated anywhere in Florida for private employers.

Citation: Fla. Stat. 448.106(1)(b), (1)(c), (2)(a), (2)(b), (3), (4), created by s. 1, ch. 2024-80 (CS/CS/HB 433)

The Florida Senate, 2025 Florida Statutes, s. 448.106last read 6 August 2026

In force from 1 July 2024

FloridaHeat and outdoor work

Federal general duty clause is the only binding heat obligation, and it carries no numbers

Binding law

Under the general duty clause, Section 5(a)(1) of the Occupational Safety and Health Act of 1970, employers must furnish employees a place of employment free from recognized hazards that are causing or likely to cause death or serious harm. OSHA treats excessive heat as such a hazard, but there is no federal heat standard in force, so no rest interval, water volume, shade requirement or temperature trigger is prescribed by binding rule.

Who this covers

Private sector employers in Florida under federal OSHA jurisdiction. Indoor heat is covered on the same basis. Does not reach Florida state and local government employees, who are outside federal OSHA coverage.

How to encode this in a schedule

The obligation is binding but supplies no encodable number. Any heat rest cycle applied to a Florida schedule is employer policy. The useful product behaviour is to surface exposure rather than block it: flag long uninterrupted outdoor blocks in the hottest hours during the Florida summer, and let the employer configure the recovery pattern.

Heat trigger basis:
none: the duty is outcome-based and states no threshold

The mistake employers make

Citing OSHA's Water, Rest, Shade campaign or its heat National Emphasis Program as if either created a duty on employers. Neither is a standard. The campaign is advisory, and the NEP (CPL 03-00-024, reissued and current as of 10 April 2026) directs OSHA area offices and inspectors on where to target inspections; it does not itself impose a scheduling obligation. Note the correction: the NEP is CURRENT, not withdrawn, so an employer scheduling outdoor summer work in Florida faces a live, targeted inspection posture even though the binding duty remains the numberless general duty clause.

Why this figure does not travel

Same duty, same wording and same absence of numbers as us-federal-heat-general-duty-clause; the two entries are the same law seen from two files. Do not double count them when tallying binding heat obligations.

Citation: Occupational Safety and Health Act of 1970, Section 5(a)(1), 29 U.S.C. 654(a)(1)

U.S. Occupational Safety and Health Administration, Heat: Standardslast read 6 August 2026

FloridaHeat and outdoor work

No Florida OSHA plan, and no federal OSHA coverage for public employees

No requirement

Florida has no OSHA-approved State Plan, so federal OSHA has direct jurisdiction over most private sector workplaces in the state and there is no state occupational safety agency layered on top. OSHA states directly that in Florida 'State and local government workers are not covered by federal OSHA.'

Who this covers

Florida statewide. Federal OSHA covers most private sector workers in the state. Florida state and local government workers are not covered by federal OSHA. This entry states a jurisdictional coverage fact, not an obligation on any employer.

How to encode this in a schedule

Split the safety ruleset by employer type rather than by geography. For a Florida city or county workforce there is no OSHA-backed heat or fatigue obligation, and under Fla. Stat. 448.106(3) the only heat rule that can apply is one the subdivision adopts for itself, so its scheduler configuration is internal policy with no statutory floor from this direction.

The mistake employers make

Assuming a Florida municipal workforce inherits the same safety floor as a private employer in the same county. It does not. The private crew has the general duty clause; the city crew has whatever the city wrote down.

Why this label and not another

Re-typed from 'guidance' to 'none'. The entry states a jurisdictional coverage fact (Florida has no OSHA-approved State Plan, and state and local government workers are outside federal OSHA), which under the shared legend is a verified absence of any requirement, not a non-binding recommendation. 'guidance' implies advisory content that a scheduler might follow; there is none here.

Citation: OSHA State Plans roster, which omits Florida and states that Florida is under federal OSHA jurisdiction covering most private sector workers, and that state and local government workers are not covered by federal OSHA

U.S. Occupational Safety and Health Administration, State Planslast read 6 August 2026

United Kingdom

Split enforcement, no single agency. HSE (with local authorities, CAA, DVSA, ORR and ONR in their sectors) enforces only the regulation 28 'relevant requirements'. Rest breaks, daily rest, weekly rest and annual leave are enforced solely by the worker at an employment tribunal. The Fair Work Agency, launched 7 April 2026, is expected to take on holiday pay enforcement from 2027.

The United Kingdom answers the most-searched heat question in the least satisfying way: there is no maximum working temperature, on any measurement basis, anywhere in the law. The widely repeated figures of 30C, or 27C for strenuous work, come from campaign material rather than legislation. The one temperature duty the Workplace Regulations do contain covers a reasonable temperature in workplaces inside buildings, which by its own terms does not reach outdoor work at all, and the 16C figure people sometimes cite is a suggested indoor minimum with nothing to say about heat.

What is missing is the number, not the obligation. The risk assessment duty in the Management of Health and Safety at Work Regulations is binding, criminally enforceable, and applies indoors and outdoors alike, and employers with 5 or more employees must record the significant findings. For a scheduling system that means the trigger temperature is a configurable field rather than a constant, and the useful thing to store next to it is which assessment the setting came from.

United KingdomHeat and outdoor work

No statutory maximum working temperature

No requirement

There is no maximum workplace temperature in Great Britain and no legal temperature at which work must stop. HSE states plainly that 'There is no maximum temperature for workplaces'. Regulation 7 of the Workplace (Health, Safety and Welfare) Regulations 1992 requires only that 'during working hours, the temperature in all workplaces inside buildings shall be reasonable', so it does not reach outdoor work at all. For indoor work HSE suggests minimum temperatures of at least 16C, or 13C if much of the work involves rigorous physical effort. For outdoor work HSE's position is that employers must provide protection from adverse weather, and for hot conditions HSE advises measures such as rescheduling work to cooler times of the day, more frequent rest breaks, shaded rest areas, free access to cool drinking water, and letting workers remove PPE when resting.

Who this covers

All workplaces, indoor and outdoor, across Great Britain. There is no temperature at which work must stop by law, and no separate outdoor temperature standard.

How to encode this in a schedule

Do not encode a stop-work temperature threshold, because none exists in UK law and a hard-coded number would misstate the position. The correct encoding is a soft, employer-configurable heat policy: a trigger temperature the employer chooses from its own risk assessment, which then shifts outdoor assignment blocks toward cooler parts of the day, increases break frequency, and requires shaded rest coverage. The 16C and 13C figures are indoor minimum-temperature guidance, not scheduling limits, and are suggestions rather than binding numbers.

Suggested minimum indoor C
16
Suggested minimum indoor strenuous C
13
Heat trigger basis:
none: UK law states no maximum working temperature on any measurement basis

The mistake employers make

Repeating the widely believed claim that work must stop at 30C, or 27C for strenuous work. Those numbers appear in trade union campaign material, not in law. The genuine legal position is the opposite of a bright line: no maximum exists anywhere in UK law, and the employer's obligation runs through risk assessment instead. Note also that regulation 7 of the 1992 Regulations only requires a reasonable temperature in workplaces inside buildings, so the one temperature duty that does exist in the Regulations does not apply to outdoor work.

Why this figure does not travel

heatTriggerC null means no threshold exists in law, not that heat is unregulated: the duty lives in uk-heat-outdoor-risk-assessment-duty and is criminally enforceable. This is the same shape as the two OSHA general-duty entries.

Why this label and not another

Re-typed from 'guidance' to 'none'. The rule's claim is a verified absence: no maximum working temperature exists anywhere in UK law. The 16C and 13C figures it also carries are HSE suggestions about indoor MINIMUM temperatures and are irrelevant to heat; they are retained for reference but they are not the subject of the rule. The binding heat obligation is carried separately as uk-heat-outdoor-risk-assessment-duty.

Citation: HSE guidance, Temperature in the workplace: what the law says, sitting alongside the Workplace (Health, Safety and Welfare) Regulations 1992 (SI 1992/3004) regulation 7

Health and Safety Executivelast read 6 August 2026

United KingdomHeat and outdoor work

Duty to risk assess heat, indoors and outdoors

Binding law

Every employer must make a suitable and sufficient assessment of the risks to the health and safety of employees while at work, and of risks to persons not in their employment arising out of the conduct of the undertaking, and must implement the preventive and protective measures identified. The assessment must be reviewed if there is reason to suspect it is no longer valid or there has been a significant change. HSE classes heat as a hazard and states that employers must assess the risks and put controls in place. Where a young person is employed the assessment must additionally take particular account of their inexperience, immaturity and lack of awareness of risk.

Who this covers

Every employer, and every relevant self-employed person, for all work activities. The duty is not limited to indoor workplaces. Employers with five or more employees must record the significant findings and any group of employees identified as being especially at risk.

How to encode this in a schedule

Not a numeric constraint on shift shape, but the legal source of every heat control a scheduler does encode. Because the duty is outcome-based rather than threshold-based, a compliant scheduling system should let the employer configure its own heat triggers and controls (cooler-hours assignment, break frequency, rotation off hot tasks, shade and water coverage) and should record which assessment those settings derive from.

Record threshold employees
5
Heat trigger basis:
none: the duty is outcome-based and states no threshold

The mistake employers make

Concluding from the absence of a maximum temperature that there is no heat duty at all. The duty is real, criminally enforceable and not confined to indoor workplaces. What is absent is the number, not the obligation.

Why this figure does not travel

Binding but numberless, the same family as us-federal-heat-general-duty-clause and us-florida-heat-outdoor-osha-general-duty. Three of the six jurisdictions regulate heat exclusively this way.

Citation: Management of Health and Safety at Work Regulations 1999 (SI 1999/3242) regulation 3(1), 3(2), 3(3), 3(4), 3(5) and 3(6)

legislation.gov.uklast read 6 August 2026

Acclimatisation, and the week that resets it

Acclimatisation is the physiological adjustment that lets a body work in heat it could not tolerate a week earlier: sweating starts sooner, sweat carries less salt, and the cardiovascular load of the same task falls. It is also the reason heat injuries cluster in the first days of a job rather than on the hottest day of the year. Someone who has worked the same outdoor post all summer is not the person at risk. The new hire on day two is, and so is the veteran back from a fortnight away.

Only one live duty in this set says so. Singapore requires a graduated increase in daily heat exposure over at least 7 days for outdoor workers new to the country and for anyone returning from leave of more than 7 days, in every WBGT band including the lowest, and it deliberately prescribes no percentage ramp. The proposed United States standard would treat an absence of more than 14 days the same way and does offer percentages, starting at 20 percent of a normal shift on day one, but it is dormant and those figures must not be borrowed to fill in Singapore's.

For a scheduler this is not a per-shift check, it is per-worker state. A returning worker needs a graduated-exposure capacity for each of their first days back rather than a binary available flag, and the window has to re-open automatically after long leave. The failure mode is almost always the same: the ramp is implemented once at onboarding and never again, so the roster treats a worker returning from a two-week absence as fully acclimatised on their first afternoon back.

How heat turns into rotation

Almost none of these rules change who is on the schedule. They change how long any one person stays in one place, which is a decision the weekly roster is the wrong instrument to make. The roster is published days ahead; the trigger is measured on the morning. So heat lands on the layer underneath, where intrashift scheduling moves people between positions and inserts non-working intervals inside a shift that is already assigned.

Singapore makes the arithmetic explicit. At WBGT 32C a shaded interval of at least 10 minutes has to appear inside every clock hour for heavy outdoor work, which is 17 percent of the hour gone, and at 33C it becomes 15 minutes, or 25 percent. Add the hourly hydration point from 31C and the recommended 300mL of water per hour, and a hot afternoon needs materially more people on site to deliver the same productive coverage. California's agricultural cadence is coarser at 10 minutes every 2 hours above 95F, but it is mandatory, and its high-heat procedures add a supervision constraint of one observer per 20 employees or a buddy system, which is a rostering decision rather than a break.

The operational answer to all of it is the same lever: shorten the interval before anyone rotates off the hot position. A staggered rotation that hands the exposed post over every thirty minutes instead of every two hours delivers the same coverage with a fraction of the individual exposure, and it does it without adding a single hour to the schedule. Where the shortest rotation still leaves someone in the sun too long, the next lever is the clock: moving the work itself into the cooler hours is what the United Kingdom's guidance points employers at, and it is the only control that reduces exposure rather than redistributing it.

One planning note that applies everywhere. A cool-down rest in California is employee-initiated and unbounded in number, with the 5-minute minimum acting as a floor rather than the entitlement, and the rest continues until symptoms abate. A roster that budgets exactly 5 minutes per person has under-planned. Heat rules of that shape are capacity constraints, not calendar entries, and they belong in the coverage buffer rather than in the shift template.

Common questions

Is there a legal maximum working temperature?
In none of the 6 jurisdictions on this page does the law name a temperature at which outdoor work must stop. The United Kingdom is explicit that no maximum workplace temperature exists. California, Japan and Singapore all have numeric triggers, but every one of them switches on a protective measure such as shade, a rest interval or a response procedure rather than switching off the work. Any policy that promises a stop-work temperature is employer policy, not law.
Does the United States have a federal heat standard?
No. A federal heat standard was proposed in August 2024 and is still a proposal, so its 80F initial trigger, its 90F high heat trigger and its 15-minute break every 2 hours impose no obligation on anyone today. The binding federal obligation is the general duty clause, which requires employers to control recognised hazards and states no threshold. Separately, OSHA's National Emphasis Program directs inspection attention on days when the heat index is expected to reach 80F, which changes inspection probability rather than the schedule.
What is WBGT, and why do heat rules use it instead of a thermometer?
Wet bulb globe temperature is a composite reading that folds humidity, radiant heat and air movement into one figure, which is why Japan and Singapore build their triggers on it. A dry-bulb thermometer reports air temperature only, so it reads the same at 30 percent humidity and at 90 percent humidity even though the body can shed heat in one case and not the other. Because WBGT includes variables a thermometer ignores, there is no fixed conversion between a WBGT figure and a dry-bulb or heat-index figure, and a site cannot infer one from the other.
What does Japan's 2025 heat rule actually require?
A reporting route and a written response procedure, in place and communicated before hot work starts. The employer must have a system for workers to report heatstroke symptoms in themselves or a colleague, and must decide in advance how the site removes someone from the work, cools them and obtains medical help. It applies at WBGT 28C or air temperature 31C where the work runs 1 continuous hour or more, or more than 4 hours across the day, and it covers indoor work as well as outdoor. It does not mandate a rest break.
Are Singapore's WBGT rest breaks legally binding?
They sit in an unusual position. The Ministry of Manpower states them as required measures, inspects against them, and non-implementation can attract stop-work orders and composition fines under the Workplace Safety and Health Act. But the 32C and 10-minute figures appear in a framework document rather than in legislation, and the binding instrument behind them is a general duty with no numbers in it. This engine records them as official guidance because of where the numbers come from, not because following them is optional. Schedule to them.
Do Florida employers have to give heat recovery breaks?
No Florida law requires one, and since 1 July 2024 no Florida county or city may require one either. That is not an exemption from heat obligations: the federal general duty clause still applies to private employers, and it is enforced case by case with no number attached, so a long uninterrupted outdoor block in the hottest hours of a Florida July remains exposed even though no ordinance may set a recovery interval.
Who needs heat acclimatisation, and for how long?
Singapore's framework requires a graduated increase in daily heat exposure over at least 7 days for outdoor workers new to the country and for anyone returning from leave of more than 7 days, at every WBGT band including the lowest. The returning-worker half is the part teams forget, because acclimatisation is usually implemented once at onboarding and never re-opened. The proposed United States standard would treat absence of more than 14 days the same way and offers a percentage ramp starting at 20 percent of a normal shift, but it is dormant and its percentages must not be used to fill in Singapore's.

Where to go next

Heat is one topic of seven in this reference. The jurisdiction pages carry the break, hours, night work and minors rules alongside these, and the methodology sets out how each figure was sourced, what the three labels mean and why several jurisdictions are deliberately absent.

Japan rules →Singapore rules →California rules →United States (federal) rules →Florida rules →United Kingdom rules →

Your next schedule could take 2 minutes.

Import your team, set your rules, hit auto-fill. Most teams are live the same day.

Try Soon free→

30 days free ยท No credit card required

Already have an account?Sign in