What Is the Hierarchy of Controls in Workplace Safety?

The hierarchy of controls ranks five ways to reduce a workplace hazard. From best to worst, they are elimination, substitution, engineering controls, administrative controls and personal protective equipment (PPE). The U.S. National Institute for Occupational Safety and Health (NIOSH) says to work from the top down. Use the strongest option that is practical.

The five levels, from strongest to weakest

Elimination removes the hazard at its source. A process might change so that a toxic chemical, a heavy object or a sharp tool is no longer needed. With the hazard gone, no one can be exposed.

Substitution swaps the hazard for something less harmful. NIOSH says a good substitute lowers the risk of harm and creates no new risks. So a replacement needs checking, not just choosing.

Engineering controls keep the hazard away from workers. They change the equipment or the workspace. Barriers, machine guards and ventilation are common examples. They work even when a worker forgets to do something.

Administrative controls change how people work. They cut how long, how often or how strongly workers are exposed. Training, job rotation and rest breaks belong here.

Personal protective equipment is worn by the worker. Examples are gloves, safety glasses, hearing protection, hard hats and respirators.

Why the order matters

The top three levels do not depend much on human behavior. They keep working on a bad day, a busy shift or a new hire’s first week. The bottom two depend on people. NIOSH says they need steady effort from workers and supervisors. PPE protects only when it is used correctly every time. A workplace that relies mainly on training and gloves is betting that everyone gets it right, always.

Cost points the same way over time. Engineering controls can cost more at the start. But NIOSH says their running costs tend to be lower, especially when many workers are protected. Earlier NIOSH guidance said administrative controls and PPE can be cheap to set up but very costly to sustain.

Design stage or existing process

Elimination and substitution are easiest at the design stage of a process, tool or workplace. They are hardest to add once work is under way. This is the idea behind NIOSH’s Prevention through Design initiative. It builds safety into designs from the start. The best time to apply the hierarchy is when new equipment or procedures are chosen.

When the lower levels are the right answer

The hierarchy is an order of preference. It does not ban the bottom levels. NIOSH says employers must provide PPE when other controls cannot bring exposure down to safe levels. They must also provide it while other controls are still being built. Some jobs need a mix. NIOSH gives one example: ventilated hoods plus PPE when preparing chemotherapy drugs. The goal is to use the highest level that works. Then add lower levels for whatever risk remains.

NIOSH is a U.S. agency. Its guidance describes a preferred order, not a legal rule. What a workplace must do by law depends on the country and its regulator. For related terms, see the entries on the hierarchy of controls, hazard identification, the risk assessment matrix and lockout tagout.

FAQs

What is the most effective control in the hierarchy? Elimination. It removes the hazard, so no exposure can occur.

Is PPE a bad control? No. It is the last line of defense. Use it when higher controls cannot cut exposure enough, or are not yet in place. It should not be the only control when better ones exist.

Why does substitution rank below elimination? Substitution still leaves a hazard in the workplace, only a smaller one. The replacement must also create no new risks.

Who publishes the hierarchy of controls? NIOSH, part of the U.S. Centers for Disease Control and Prevention, publishes a widely used version. It promotes the hierarchy as part of Prevention through Design.