Why safety is a numbers game
You can only improve health and safety performance if you measure it consistently, and the same handful of formulas underpins almost every serious safety dashboard. This guide walks through the 37 calculations and explains what each one tells you, and shows what it is used for.
The formulas fall into ten groups: injury rates, workforce exposure, audit and compliance, risk, emergency readiness, behavioural observations, contractors, leading and lagging indicators, additional rates, and the mindset that ties them together. Numbers do not make a workplace safe by themselves. Used well, they show where the gaps are, whether controls are working, and where to spend time and money next.
Before you calculate: pick your basis and definitions
Two companies can report very different accident rates for the same performance simply because they use different multipliers or definitions. Settle three things before you compare any number.
- The multiplier. Rates are scaled so that small and large organisations can be compared fairly.
- The definition of each case type. What counts as a lost time injury, a recordable case or a restricted work case varies between organisations, clients and regulators.
- The denominator. Hours worked is the most accurate exposure measure. Headcount or estimated hours are weaker substitutes.
| Multiplier | Typical use | What it represents |
|---|---|---|
| 200,000 hours | US OSHA-style rates such as TRIR and DART | About 100 full-time employees working a year |
| 1,000,000 hours | LTIFR, frequency rate, near-miss rate, and many international client and industry reports | One million hours of exposure |
| 100,000 workers | UK HSE national statistics, which are expressed per 100,000 employees rather than per hours | A standardised workforce size |
Always follow the basis your client, industry body or reporting system specifies, and state the basis next to every figure you publish.
1. Safety performance: injury and incident rates
These eight rates turn raw injury counts into comparable figures. They are the core of most client and board safety reports.
Frequency Rate (FR) shows how often lost time injuries (LTIs) occur per million hours worked. Use it to track whether injuries are becoming more or less common over time.
- FR = LTIs x 1,000,000 / Man-hours worked
Severity Rate (SR) shows how many working days are lost per million hours. It tells you how serious injuries are, not just how many there are. Divide SR by FR (on the same basis) to get the average days lost per lost time injury.
- SR = Lost workdays x 1,000,000 / Man-hours worked
Lost Time Injury Frequency Rate (LTIFR) is the most widely quoted headline measure in contractor pre-qualification and tender questionnaires.
- LTIFR = LTIs x 1,000,000 / Hours worked
Total Recordable Incident Rate (TRIR) counts every recordable case, not only those that cost working days. It gives a fuller picture of injury performance than LTIFR and is standard in US-linked and oil and gas supply chains.
- TRIR = Recordable cases x 200,000 / Hours worked
DART Rate covers cases involving days away from work, restricted work or job transfer. It highlights injuries serious enough to change what a person can do at work.
- DART = DART cases x 200,000 / Hours worked
Lost Workday Case Rate (LWDC) counts only cases where the person was away from work, which makes it a narrower, stricter measure than TRIR.
- LWDC = LWDC x 200,000 / Hours worked
Incident Rate applies the same approach to all incidents, so it can include damage-only events and other non-injury incidents depending on how you define an incident.
- Incident Rate = Number of incidents x 200,000 / Hours worked
Near-Miss Rate measures how many near misses are reported per million hours. Unlike the other rates, a higher figure here is often a good sign, because it suggests people are reporting events that could have caused harm.
- Near-miss Rate = Near misses x 1,000,000 / Man hours worked
2. Man-hours and workforce: measuring exposure
Every rate in the previous section depends on one number: hours worked. Get this wrong and every other figure is wrong with it.
Man-hours worked is the total exposure for a period. Use actual hours, including overtime and agency or temporary labour, and exclude leave and sickness.
- Man-hours = Workers x Working hours x Working days
Average workforce converts total hours back into an equivalent number of full-time people. It is useful when headcount changes during the year, for example on a project that ramps up and down.
- Average workforce = Total man-hours worked in the period / Standard working hours per person in the period
Safe man-hours % shows the proportion of hours worked without a recordable or lost time injury. It is a positive, easy-to-communicate measure for site boards. Many organisations instead report a running total of safe man-hours since the last lost time injury, so check which version your audience expects.
- Safe man-hours % = Safe man-hours / Total man-hours x 100
Absenteeism % measures the share of available working days lost to absence. It is a workforce health indicator rather than a pure safety measure, but a sustained rise can point to fatigue, stress, poor welfare or underlying health problems worth investigating.
- Absenteeism % = Absent man-days / Available man-days x 100
3. Audit and compliance: are the controls actually in place?
Six compliance percentages share one structure: what was found compliant, divided by what was checked, multiplied by 100. They show whether your management system is working in practice, not just on paper.
| Metric | Formula | What it tells you |
|---|---|---|
| Audit compliance % | Compliant points ÷ applicable points × 100 | Overall conformity with the audit protocol or standard |
| PPE compliance % | Compliant workers ÷ workers checked × 100 | Whether PPE rules are followed in the field |
| Permit to work (PTW) compliance % | Compliant permits ÷ permits audited × 100 | Quality and discipline of high-risk work control |
| CAPA closure % | Closed actions ÷ total actions × 100 | Whether corrective and preventive actions are actually completed |
| Training compliance % | Trained employees ÷ applicable employees × 100 | Coverage of mandatory and role-specific training |
| Inspection compliance % | Completed inspections ÷ planned inspections × 100 | Whether the inspection programme is being delivered |
Three habits make these figures more trustworthy:
- Define “applicable”. Exclude items that genuinely do not apply, and record why.
- Report sample size. A PPE result based on 8 workers is not the same as one based on 80.
- Track overdue actions separately. A high CAPA closure rate can hide a handful of serious actions that have been open for months.
4. Risk management: scoring and comparing risk
Risk calculations let you rank hazards, justify the controls you choose and show that those controls made a measurable difference.
Risk score multiplies the likelihood of harm by its severity, usually on a 5 × 5 matrix. It lets you prioritise: a score of 20 needs attention before a score of 6.
- Risk score = Likelihood x Severity
Residual risk is the risk that remains after controls are in place. It is scored the same way, using the likelihood and severity you expect with the controls working. If residual risk is still high, you need further controls, or you need to stop the activity.
Risk reduction % shows how much the controls achieved compared with the starting position. It is useful evidence in risk assessments, management reviews and client reports.
- Risk reduction % = Initial risk – Residual risk /Initial risk x 100
Worked example. A manual handling task is scored at likelihood 4 and severity 4, giving an initial risk of 16. After introducing a mechanical aid and training, likelihood falls to 2 while severity stays at 4, so residual risk is 8. Risk reduction is (16 − 8) ÷ 16 × 100 = 50%.
Remember that a risk score is a judgement made visible, not a measurement. Use the same scoring criteria every time, and have more than one competent person agree the scores for significant risks.
5. Emergency and fire safety: how ready are you?
Three measures test whether your emergency arrangements work when it matters. They are most useful when taken from real drills and real events, not estimated.
Emergency response time is the gap between notification of an emergency and the start of an effective response. Shorter is better, and trends across drills show whether response is improving.
- Response time = T effective response – T notification
Evacuation time is how long it takes for everyone to reach the assembly point after the alarm sounds. Compare it with the target in your fire risk assessment and emergency plan, and look at what slowed people down: blocked routes, unclear signage, people with mobility needs, visitors or contractors who are unfamiliar with the site.
- Evacuation time = T assembly complete – T alarm
Fire extinguisher coverage compares the extinguishers you need with those you actually have in place and in working order.
- Extinguisher coverage % = Available and compliant extinguishers / Required extinguishers x 100
The number required should come from your fire risk assessment, using recognised guidance on selecting and siting portable extinguishers. Anything below 100% is a gap to close, and “compliant” should include being in the right place, correctly signed, and in date for servicing.
6. Safety observations and behaviour: what the front line is telling you
Observation programmes generate a lot of data. Four simple percentages turn it into something you can act on.
| Metric | Formula | What it tells you |
|---|---|---|
| Observation closure % | Closed observations ÷ total observations × 100 | Whether issues raised are being fixed, which drives trust in the programme |
| Unsafe act % | Unsafe acts ÷ total observations × 100 | How often people are seen working in an unsafe way |
| Unsafe condition % | Unsafe conditions ÷ total observations × 100 | How often the workplace itself is found to be unsafe |
| Repeat observation % | Repeat observations ÷ total observations × 100 | Whether the same problems keep coming back |
Read them together rather than in isolation:
- A high unsafe act % with a low unsafe condition % points towards supervision, training, workload or culture.
- A high unsafe condition % points towards maintenance, housekeeping, equipment and design.
- A high repeat observation % is a warning that actions are closing on paper without fixing the root cause.
- A low closure rate suggests workers will stop reporting, because nothing seems to happen.
Be careful not to treat a falling unsafe act percentage as proof of improvement. It can also mean observers are less thorough, or that people behave differently when they know they are being watched. Check the trend against near-miss reports and inspection findings.
7. Contractor safety: holding the supply chain to the same standard
Contractors often carry a large share of the risk on a site, and clients increasingly ask for contractor-specific figures. Three measures cover the basics.
Contractor incident rate applies the TRIR approach to contractor workers only, using their own recordable cases and their own hours. Keeping it separate stops good employee performance from masking contractor problems, or the reverse.
- Contractor incident rate = Contractor recordable cases x 200,000 / Contractor hours worked
Contractor compliance % shows how many of your site requirements contractors are meeting, such as method statements, competence evidence, permits, insurance and inspection of work equipment.
- Contractor compliance % = Compliant contractor requirements / Applicable requirements x 100
Induction compliance % checks that everyone on site has been inducted before starting work. Anything below 100% means someone is working without knowing the site rules, emergency arrangements or hazards.
- Induction compliance % = Inducted workers / Total mobilised workers x 100
On construction projects, the Construction (Design and Management) Regulations 2015 place duties on clients, principal designers and principal contractors that relate directly to these measures, including site inductions and checking contractor competence. Contractor figures are also a practical way to evidence that duty-holders are managing the people they bring onto site.
8. Leading and lagging indicators: look ahead as well as back
Safety performance is the combination of leading indicators, which measure the effort you put into preventing harm, and lagging indicators, which measure the harm that has already happened. Relying on lagging indicators alone is like driving by looking only in the rear-view mirror.
Leading indicators (proactive)
- Safety inspections completed
- Training hours delivered
- Safety observations made
- Toolbox talks held
- Audits completed
- Mock drills carried out
- Near-miss reports submitted
- CAPA closure
Lagging indicators (reactive)
- Fatalities
- Lost time injuries
- Recordable injuries
- Lost workdays
- Occupational illnesses
Lagging indicators matter because they are the outcomes you are ultimately trying to prevent, and many are legally reportable. Their weakness is that they are often too few to be statistically meaningful, especially in a small or medium-sized business. A year with zero injuries may reflect good control or simply good luck.
Leading indicators fill that gap by showing, month by month, whether the activities that prevent harm are actually happening. Most of the percentages in sections 3, 6 and 7 are leading indicators. A good dashboard pairs each lagging result with the leading measures most likely to influence it.
9. Additional formulas: recordable rates and environmental performance
Four environmental measures that matter for sustainability reporting and ISO 14001-style environmental management can also be considered.
Total Recordable Incident Rate (TRIR), expanded. This is defined as fatalities plus lost time injuries plus restricted work cases. Be aware that the full OSHA definition of a recordable case also includes medical treatment beyond first aid, so confirm which cases your client counts.
- TRIR = (Fatalities + LTIs + Restricted work cases) x 200,000 / Hours worked
Days Away, Restricted or Transferred (DART). This adds up cases where someone was away from work, on restricted duties or moved to a different job. Count cases, not days.
- DART = (Days-away + Restricted + Transferred cases) x 200,000 / Hours worked
Environmental incident rate tracks spills, uncontrolled releases, permit breaches and similar events against hours worked, so you can see whether environmental control is improving as the workload changes.
- Environmental incident rate = Environmental incidents x 200,000 / Hours worked
The last three are intensity measures. They divide resource use by output, which shows efficiency rather than just total consumption. If production doubles and energy use rises by 50%, intensity has improved even though the total went up.
| Metric | Formula | Example unit |
|---|---|---|
| Energy consumption rate | Energy used ÷ output | kWh per unit produced |
| Water consumption rate | Water used ÷ output | m³ per unit produced |
| Waste generation rate | Waste generated ÷ output | kg per unit produced |
Choose an output measure that suits your business, such as units produced, tonnes processed, turnover, or hours of service delivered, and keep it the same from year to year so trends are meaningful.
10. The HSE mindset: from numbers to decisions
The formulas only matter if they feed a cycle of improvement which has six steps:
- Identify hazards and risks.
- Assess and prioritise them.
- Control them by putting safeguards in place.
- Measure performance with the formulas in this guide.
- Analyse gaps and trends.
- Improve controls and build a stronger safety culture, then go round again.
Five practical points keep the numbers honest:
- Fix your definitions. Write down what counts as an LTI, a recordable case, a near miss and an incident, and apply it consistently.
- State your basis. Say whether a rate is per 200,000 or 1,000,000 hours, and which period it covers.
- Protect data quality. Late reporting, missing hours and inconsistent classification distort every rate.
- Use numbers to decide, not just to report. Each metric should prompt a question about what to do next.
- Combine data with walking the site. Numbers show where to look, and conversations with the workforce explain why.
Turning the numbers into better safety
Good safety measurement is consistent, clearly defined and tied to action. Start with the few metrics that match your risks, such as hours worked, a recordable injury rate, near-miss reporting, action closure and training compliance, and build from there.
If you require help identifying legislation applicable to your workplace, please contact one of our team.
