What Is Hazard Analysis?

Hazard analysis is the systematic process of identifying conditions or situations that could cause harm, characterizing the nature and magnitude of that harm, and informing decisions about how to reduce or eliminate the associated risk. It is a foundational discipline in safety engineering, applied wherever the failure of a system or process could injure people, damage property, or harm the environment. The practice draws from systems theory, reliability engineering, and occupational safety science.

The distinction between hazard and risk is central to hazard analysis. A hazard is a potential source of harm; risk is the product of the probability that the hazard will cause harm and the severity of that harm. Hazard analysis addresses the identification and characterization step; risk assessment and risk reduction follow from it.

Hazard Identification

The first task in any hazard analysis is to enumerate all credible hazard scenarios associated with a system. This is harder than it appears: systems have interactions among components that are individually benign but hazardous in combination, and the space of possible failure sequences grows quickly with system complexity. Structured elicitation methods such as HAZOP (Hazard and Operability Study) and What-If Analysis guide analysts through systematic examination of process parameters and their deviations. HAZOP, which originated in the chemical and process industries, applies guide words to each design parameter to surface scenarios designers may otherwise overlook.

Preliminary Hazard Analysis (PHA) is often performed early in a design program, before detailed specifications are complete, to identify major hazard categories and constrain subsequent design decisions. The System Safety Society maintains professional standards and guidance for PHA and related methods used in defense and aerospace programs.

Severity and Likelihood Assessment

Once hazards are identified, each is characterized along two axes: the severity of the harm it could produce and the likelihood of occurrence. Severity categories typically range from catastrophic (fatalities or total system loss) through critical and marginal to negligible. Likelihood categories range from frequent to improbable. The combination of these two dimensions produces a risk level that is compared against acceptance criteria specified by the applicable safety standard.

Quantitative estimates of likelihood draw on reliability data, historical incident statistics, and probabilistic modeling. Fault Tree Analysis (FTA) and Event Tree Analysis (ETA) are quantitative methods used to compute the probability of top-level hazard events from component failure rates. The NIST system safety and reliability resources provide statistical foundations relevant to these probability calculations.

Risk Reduction and Verification

The output of hazard analysis is a set of recommendations or requirements for risk reduction. Controls are applied according to a hierarchy: design changes that eliminate the hazard are preferred over safeguards that mitigate it, and safeguards are preferred over warnings and procedures. The analysis is revisited when design changes are made, because modifications can introduce new hazards or invalidate previous assessments.

Verification involves demonstrating that implemented controls achieve the required risk reduction. This may involve testing, simulation, inspection, or formal verification, depending on the nature of the hazard and the governing standard. The IEC 61508 standard for functional safety specifies verification requirements for safety-critical electrical systems.

Applications

Hazard analysis is applied across a wide range of safety-critical domains, including:

• Aerospace vehicle and systems certification
• Chemical process and nuclear plant safety
• Medical device risk management
• Road vehicle functional safety under ISO 26262
• Industrial machinery and workplace safety programs
• Software systems in safety-critical control applications