Safety management heuristic

Heinrich's Law

Treat small incidents as warning lights, not background noise.

Popularity

Usefulness

Aliases

Heinrich's Triangle / Accident Triangle / Safety Triangle / Safety Pyramid / Accident Pyramid / 300-29-1 Rule

Domains

Occupational safety, industrial safety, risk management, accident prevention, workplace health and safety

Definition

Heinrich's Law is a workplace safety rule-of-thumb stating that, for every 1 major injury accident, there are about 29 minor injury accidents and 300 no-injury accidents or near-miss events. It is usually shown as a triangle or pyramid. (SKYbrary)

Serious accidents are often preceded by many smaller incidents, unsafe conditions, or near misses.
Preventing and learning from low-severity incidents may reduce the likelihood of severe accidents.
The 300:29:1 ratio should be treated as an illustrative pattern, not a universal mathematical law.

Accidents are grouped by severity:
- 300 no-injury accidents / near misses
- 29 minor injury accidents
- 1 major injury accident
The rule suggests that many events share underlying hazards or causes.
By investigating near misses and minor incidents early, an organization can identify hazards before they produce serious harm.
Modern use focuses less on the exact ratio and more on proactive reporting, hazard removal, and system improvement.

In a warehouse, workers report frequent pallet near misses, minor slips, and forklift blind-spot problems.
Instead of waiting for a serious injury, management investigates the pattern, improves traffic routes, adds mirrors, retrains operators, and redesigns loading zones.
This applies Heinrich's Law by treating small warning events as signals of larger risk.

Example: No verified single famous example found.
Why it fits this rule: Heinrich's Law is commonly illustrated with generic workplace accident patterns rather than one consistently verified historical case.
Verification status: No verified example found; the 300:29:1 ratio itself is historically associated with Heinrich's 1931 safety work, but many popular examples are generic or uncited.

Near-miss reporting programs
Factory, construction, warehouse, aviation, transport, and industrial safety reviews
Safety audits and hazard trend analysis
Incident investigation and root-cause analysis
Early warning systems for recurring small failures
Building a safety culture where minor events are reported instead of hidden

Do not treat 300:29:1 as a fixed natural law.
Do not assume reducing minor injuries will automatically eliminate catastrophic risks.
Do not use it to blame workers while ignoring equipment design, management systems, training, workload, incentives, and organizational causes.
Do not compare departments only by minor incident counts; low reports may mean underreporting, not safety.
Do not apply it blindly to high-hazard, low-frequency risks such as explosions, aviation disasters, major chemical incidents, or complex system failures.

Invented by: Herbert William Heinrich, an American industrial safety pioneer and safety engineer associated with Travelers Insurance Company. (Safety+Health Magazine)
Year of invention: Commonly attributed to 1931, when Heinrich published Industrial Accident Prevention: A Scientific Approach. (Google Books)
Country / context of origin: United States; industrial accident prevention and insurance-based workplace safety analysis. Heinrich reportedly reviewed 75,000 injury and illness cases, including insurance records and reports from plant managers. (Safety+Health Magazine)

Original basis: Heinrich's 1931 work proposed the 300:29:1 accident ratio after reviewing industrial accident records. (Safety+Health Magazine)
Limitation: Later critics note that Heinrich's original files are not available for independent review, and the ratio was reportedly revised in later editions without clear explanation. (Safety+Health Magazine)
Modern evidence is mixed. A 2018 study using data from more than 25,000 establishments over 13 years found support for a safety-triangle pattern, but the result depended on how incident severity was defined. (stacks.cdc.gov)
Another statistical study using more than 50,000 Chilean companies found the pyramid statistically invalid across sectors and regions, but still practically useful as a signal of overall safety performance. (ScienceDirect)
Best supported interpretation: the exact ratio is not reliable, but minor incidents and near misses can provide useful warning signals.

Treat small incidents as warning lights, not background noise.
The number 300:29:1 is less important than the habit of investigating weak signals before they become serious harm.