Definition:
Probable Loss of Life (PLL) is the number of fatalities for a given event or accident. It is not a probability and can be any number ≥ 0 including decimals. It can be applicable to an event (probable death per event) or per unit time (probable deaths per year).
Can also be called “potential loss of life” or “expected fatality rate.”
Unfortunately, the industry does not use this term consistently. This is the approach we at SIL Safe use. Some use the term “probability of loss of life” but even then they don’t treat it as a probability, which is confusing.
Key Points:
- Used in quantitative risk assessments.
- Can drive decisions about SIL levels and mitigation measures.
- PLL is typically summed across all hazards at a facility to represent the total expected loss of life.
Example:
The PLL for a chemical facility is 1E-5/year means one expected fatality every 100,000 years of operation. Meanwhile, another facility may have a PLL of 22.6 for a given explosion scenario, meaning around 23 people are expected to die from an explosion.
See Also: QRA, major accident
Cited Source:
- CCPS Guidelines for Chemical Process Quantitative Risk Analysis.
- NTNU – Norwegian University of Science and Technology – training slides pg 12