Calculate cumulative safe man hours from average workers and hours worked, or find workers or hours needed when two values are known.
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Cumulative Safe Man Hours Formula
The cumulative safe man hours calculation estimates the total man-hours worked during a period with zero lost time injuries, often written as 0 LTIs. The main formula is:
- SH = cumulative safe man hours
- N = average number of workers during the period
- H = average hours worked per worker during the period
If you know cumulative safe man hours and average hours per worker, you can calculate the average number of workers:
If you know cumulative safe man hours and average number of workers, you can calculate the average hours worked per worker:
The calculator works by using any two of the three values to solve for the missing one. Enter workers and hours to calculate safe man hours, enter safe man hours and hours to calculate workers, or enter safe man hours and workers to calculate average hours per worker.
Common Inputs for Safe Man-Hour Tracking
Use the table below as a quick check for typical man-hour calculations. The values are examples only and assume no lost time injuries during the full period.
| Average Workers | Hours per Worker | Cumulative Safe Man Hours |
|---|---|---|
| 25 | 160 | 4,000 |
| 50 | 200 | 10,000 |
| 100 | 180 | 18,000 |
| 250 | 160 | 40,000 |
How to Interpret the Result
| Result | Meaning |
|---|---|
| SH | Total labor hours completed during the injury-free period. |
| N | Estimated average number of workers needed to produce the stated safe man hours. |
| H | Average hours worked by each worker over the selected period. |
| 0 LTIs required | The hours are counted as safe man hours only for the period without a lost time injury. |
Example Calculations
Example 1: Calculate cumulative safe man hours
A site has an average of 75 workers. Each worker averages 160 hours during the reporting period.
The cumulative safe man hours are 12,000, assuming the period had 0 lost time injuries.
Example 2: Calculate average hours per worker
A project reports 48,000 safe man hours with an average workforce of 200 workers.
The average hours worked per worker are 240 hours.
FAQs
What counts as cumulative safe man hours?
Cumulative safe man hours are the total hours worked by employees, contractors, or site personnel during a defined period with no lost time injuries. If a lost time injury occurs, many safety tracking systems restart the count from zero or start a new reporting period.
Is this the same as total man-hours worked?
It is the same calculation only when the period has zero lost time injuries. Total man-hours worked simply measures labor time. Cumulative safe man hours measures labor time within an injury-free period, so the safety condition matters.
Should overtime be included?
Yes, overtime is usually included if those hours were actually worked during the injury-free period. The value for hours per worker should represent the average total hours worked per person, including regular time and overtime if applicable.