Posted By Alex.wilkes This depends on what you are going to calculate. Many companies assess total manhours without loss time injuries. So the calculation would be as follows. Total number of hours worked, divided by number of lost time injuries, times 1,000,000. Now total numbers of hours worked can be summarised in different ways. If you are looking at overall totat you would include all hours worked. If you are looking at doing statistics for a year then you would use the total manhours for the year, divided by number of lost time injuries for the year, times 1,000,000. This can also be assessed by things such as the number of accidents. You would simply chance lost time injuries to accidents. Many use this calculation for first aid injuries aswell. I hope this helps but I can not point you towards any documentation I am afraid. Search the www.hse.gov.uk and might find something.