Hierarchy of Controls Explained: The 5 Levels of Hazard Control

When a hazard is identified — through a HAZOP study, a PHA, or an incident investigation — the next question is what to actually do about it. The hierarchy of controls answers that question by ranking options from most to least effective.

What Is the Hierarchy of Controls?

The hierarchy of controls (also called the hazard control hierarchy or hierarchy of hazard controls) is a widely used framework, developed by NIOSH, for selecting the most effective way to protect workers from a hazard. It's structured as five levels, from most effective (removing the hazard entirely) to least effective (relying on the worker to protect themselves).

The 5 Levels of the Hierarchy of Controls

1. Elimination — physically remove the hazard entirely. The most effective control, because if the hazard doesn't exist, it can't cause harm.
2. Substitution — replace the hazard with something less dangerous, such as switching to a less toxic chemical.
3. Engineering controls — isolate people from the hazard through design, such as machine guarding, ventilation systems, or enclosed processes.
4. Administrative controls — change how people work around the hazard, through training, signage, permit to work systems, and procedures.
5. Personal protective equipment (PPE) — equip workers with gear like respirators, gloves, or hearing protection. The least effective control on its own, because it depends entirely on correct, consistent use.

Why the Order Matters

The hierarchy is ordered by reliability, not convenience. Controls higher in the hierarchy (elimination, substitution) don't depend on human behavior to work — a hazard that's been eliminated stays eliminated. Controls lower in the hierarchy (administrative controls, PPE) depend on people following procedures correctly every time, which makes them less reliable as a first line of defense. Most real-world safety programs combine multiple levels rather than relying on just one — for example, an engineering control (ventilation) paired with PPE (a respirator) as a backup.

Hierarchy of Controls in Practice

This framework underpins most modern EHS programs, including process safety management (PSM), where selecting controls for hazards identified through PHA or HAZOP always starts by asking whether the hazard can be eliminated or substituted before falling back to administrative controls and PPE.

References

• Hierarchy of hazard controls — Wikipedia
• Hierarchy of Controls — NIOSH