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High-Impact, Low-Frequency (HILF)

What Does High-Impact, Low-Frequency (HILF) Mean?

“High-impact, low-frequency” (HILF) is a term that refers to an event that happens with a low degree of frequency, usually in a manner that is irregular, unpredictable, and that causes a significant degree of disruption when it occurs. A closely related term is “high-impact, low-probability” (HILP).

Within the context of occupational safety, HILF events usually refer to rare but catastrophic incidents that result in either one or more fatalities or mass injuries, such as dust explosions or aircraft crashes. The possibility of an HILF incident is a particular concern within the process industries. For example, within the oil and gas industry, explosions and other HILF incidents at refineries and offshore platforms have been associated with numerous cases of catastrophic injury and death.

Safeopedia Explains High-Impact, Low-Frequency (HILF)

The prevention of HILF events is an important part of an overall health and safety program. Much of the prevention is undertaken through regular safety procedures, such as the regular maintenance and inspection of safety equipment within a job site. However, HILF event prevention is also the subject of dedicated safety programs and research, separate from initiatives that also include the prevention of the higher-frequency, lower-impact incidents that form the majority of health and safety incidents at work.

HILF events receive particular attention within industries where the total number of recorded injuries has decreased, while the rate of fatalities remains roughly unchanged. This disparity contradicted the classical pyramidal model of occupational safety (the Heinrich Pyramid), which predicts that a decrease in minor incidents would be concomitant with a decrease in major injuries and fatalities.

Learning to discover, predict, and adequately eliminate the causes of HILF events is therefore a major concern for industries in which HILF events are a problem. Research into construction-industry HILF events has found that it is far more difficult to predict their cause in advance than to discover it after the event occurs. Researchers have proposed models that analyze an aggregate of safety factors within a workplace to predict whether it is at risk of an HILF event. Some research has indicated that firms with a strong safety culture may avoid HILF events due to the high visibility that any unsafe work practices would receive in such a culture.

OSHA officials have testified to the U.S. Senate that the identification of leading indicators (warning signs) of impending HILF events is an ongoing challenge for many industries, and it does not have a ready solution.


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