How many first aiders should a team of 15 have?

Two covers the site on about 98.4 percent of working days, leaving roughly 4.2 days a year with no first aider present. Three covers about 99.8 percent, or 0.5 uncovered days. Which is right depends on the hazard and on whether the team works in one place, but two is the floor at which the question stops being a coin flip.

Does the size of the team change the answer?

Less than people expect. The model runs on the number of holders and how often each is absent, not on the number of colleagues around them. A team of 15 with two first aiders has the same 4.2 uncovered days as a team of 8 with two. Size matters only because bigger teams tend to spread across more places, and each place needs its own cover.

What if both first aiders are away at once?

The model puts that at about 4.2 working days a year on the assumption that their absences are independent. In reality holders who trained together often holiday in the same school weeks, so the true figure is higher. A third holder, or a rule that the two cannot book the same week, is the practical fix.

How Many First Aiders Does a Team of 15 Need?

Two first aiders in a team of 15 leave the site without one on about 4.2 working days a year. A third brings it to 0.5.

Holders2

Short working days a year4.298.4% of working days covered

Two keeps a first aider on site on 98.4 percent of working days, which is to say the site runs without one on about 4.2 days a year. That is the position most teams of 15 are in, and it is defensible. Three takes the expected gap to 0.5 days a year. The team size barely enters this arithmetic: what matters is how many people hold the certificate and how often each of them is away, and at 15 people the cost of a third course is small against the roster it protects.

Each extra holder, and what it buys

The rule says 1 first aider present on every working day. Each holder is absent on about 12.6 percent of rostered working days. This is how many working days a year fall short at each holder count.

1 holder

33 short

2 holders

4.2 shortthis page

3 holders

0.5 short

4 holders

0.1 short

5 holders

0 short

6 holders

0 short

Holding exactly 1 is a coin flipped every working day. The first spare holder removes most of the exposure; the second removes most of what is left. On these assumptions, 3 holders bring the expected shortfall to one working day a year or fewer, and 4 to one a decade.

How many are actually present

With 2 holders, the average working day has 1.75 present. Averages do not break rosters; the working days with fewer than 1 do. Across 261 working days a year, this is how the year is expected to distribute.

0 present

4.2 working daysshort

1 present

57.7 working days

2 present

199.2 working days

What is hard about this one

Fifteen is the size at which the team starts to believe it is big enough to be safe, and the belief is about the team when it should be about the holders. Thirteen of the fifteen cannot help on the day it matters. The two who can are each away on about 12.6 percent of working days, and both are away together on about 1.6 percent, which is 4.2 days a year. That is the number to carry into the next conversation about training budget, because it is small enough to defend and large enough to be real.

The argument for a third holder at this size is less about the 3.7 days it saves and more about what a third person does to the other two. With two holders, every absence by one leaves the other as the single point of failure for as long as it lasts, and a two-week holiday by one is two weeks in which the site is one sick day from uncovered. The model counts that as ordinary risk, 57.7 days a year with exactly one present, but in practice those are the weeks when the remaining holder cannot be released for anything. Three holders means the site is never one absence from empty.

Fifteen people is also where the team is big enough to be spread across more than one room, floor or building, and "on site" starts to need a definition. The binomial assumes any present holder counts. If the two holders sit in the same office and the warehouse is across the yard, the effective holder count for the warehouse is zero on most days regardless of what the roster says. Count holders per place where someone could get hurt, not per payroll, and the answer for a team of 15 is often three or four rather than two.

Move the requirement, move the answer

The holder count is usually the thing being argued about. The requirement itself is the other lever, and it is worth knowing what the same 2 holders buy if the rule were one looser or one stricter.

Required present	Covered	Short working days a year
1this page	98.4%	4.2
2	76.3%	61.8

What this assumes, and where it is generous

These figures treat each holder as independently likely to be absent, which is the assumption most favourable to the roster. Holders are rarely independent: the two people who did the course together take the same school holidays, a certificate that lapses removes someone for the weeks it takes to rebook, and the person who is always asked to cover is the one most likely to be off sick. Treat every number here as the best case.

Only a valid certificate counts. A holder whose certificate has lapsed is a zero in this arithmetic for as long as the renewal takes, so the practical holder count is often one lower than the roster believes, and the row above the one you planned for is the one you are actually living on.

The absence share is 25 days of paid annual leave and 8 days of average sickness per person across 261 working days, which is 12.6 percent of rostered working days. Both inputs vary by country; the relief factor library carries sourced figures for 17 of them. Swap your own in and the shape of the ladder holds even as the counts move.

What to do with this

Two first aiders is a defensible position for a team of 15, with an expected 4.2 uncovered working days a year; three is a comfortable one at 0.5.
Count holders per location, not per team. If the team works across two buildings, each building needs its own arithmetic.
When one holder books a fortnight off, treat the remaining one as unreleasable for that fortnight, because the site is then one sick day from uncovered on every one of those days.

How long the certificate itself stays valid, and how it is renewed: First Aid at Work (FAW) certificate (United Kingdom, 3 years), Emergency First Aid at Work (EFAW) certificate (United Kingdom, 3 years).

The holder count on this page only works if it is the count of people whose certificate is valid today. Keeping that record current, who holds what, at which level, and until when, is what the Skills tab in Soon is for.

Common questions

How many first aiders should a team of 15 have?: Two covers the site on about 98.4 percent of working days, leaving roughly 4.2 days a year with no first aider present. Three covers about 99.8 percent, or 0.5 uncovered days. Which is right depends on the hazard and on whether the team works in one place, but two is the floor at which the question stops being a coin flip.
Does the size of the team change the answer?: Less than people expect. The model runs on the number of holders and how often each is absent, not on the number of colleagues around them. A team of 15 with two first aiders has the same 4.2 uncovered days as a team of 8 with two. Size matters only because bigger teams tend to spread across more places, and each place needs its own cover.
What if both first aiders are away at once?: The model puts that at about 4.2 working days a year on the assumption that their absences are independent. In reality holders who trained together often holiday in the same school weeks, so the true figure is higher. A third holder, or a rule that the two cannot book the same week, is the practical fix.