Enter any two values into the calculator to determine the cumulative safe man-hours for an injury-free period (i.e., a period with zero lost time injuries). If a lost time injury (LTI) occurs, many organizations reset the “safe man-hours” counter at the time of the incident and start accumulating again.

Cumulative Safe Man Hours Calculator

Note: This calculator estimates cumulative safe man-hours as total man-hours worked during an injury-free period (0 LTIs).

Enter any 2 values to calculate the missing variable

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Cumulative Safe Man Hours Formula

The following formula can be used to estimate cumulative safe man-hours for an injury-free period by multiplying the average number of workers by the average hours worked per worker during that period. (If you already have the total man-hours worked for an injury-free period, that total is the cumulative safe man-hours for that period.)

SH = N \times H

Variables:

  • SH is the cumulative safe man-hours (person-hours worked with zero LTIs during the period)
  • N is the average number of workers during the period
  • H is the average hours worked per worker during the period (hours)

To estimate cumulative safe man-hours for an injury-free period, multiply the average number of workers by the average hours worked per worker during that same injury-free period. If a lost time injury occurs, the “safe man-hours” counter is typically restarted at the time of the incident and begins accumulating again afterward.

What are Cumulative Safe Man Hours?

Cumulative safe man-hours (often called accident-free man-hours) are the total number of hours worked without a lost time injury (LTI). Many organizations track this as a running counter that increases as work is performed and is reset (or restarted) when an LTI occurs. This metric is commonly used in occupational health and safety to help monitor safety performance, set goals, and communicate progress, especially in higher-risk industries such as construction, manufacturing, and mining.

How to Calculate Cumulative Safe Man Hours?

The following steps outline how to calculate the Cumulative Safe Man Hours.

  1. First, choose the injury-free period you are measuring (commonly since the last LTI, or any period with zero LTIs).
  2. Next, determine the total hours worked by each worker during that period (or the average hours worked per worker, H).
  3. Next, determine the average number of workers (N) during that period.
  4. Then, estimate cumulative safe man-hours using the formula SH = N × H (or sum the actual worked hours for all workers to get total man-hours).
  5. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Average Number of Workers (N) = 25

Average Hours Worked per Worker for the Period (H) = 40 hours

SH = N × H = 25 × 40 = 1000 safe man-hours (assuming the period had 0 LTIs).