The best way to protect a worker from a toxic chemical is to stop using it. The least reliable is to hand them a respirator and hope they wear it correctly every day. Between those two lies the hierarchy of controls, the National Institute for Occupational Safety and Health's ranked list of ways to control hazards at work. The higher an action sits, the less it depends on people doing the right thing.
The hierarchy of controls, from most effective (top) to least. Credit: National Institute for Occupational Safety and Health.
The five levels
| Level | What it does | Example |
|---|---|---|
| 1. Elimination | Removes the hazard at its source — no exposure can happen | Changing a process to stop using a toxic chemical, heavy object or sharp tool |
| 2. Substitution | Swaps in a safer alternative | Plant-based printing inks instead of solvent-based inks |
| 3. Engineering controls | Keeps hazards from reaching workers | Modified equipment or workspaces, protective barriers, ventilation |
| 4. Administrative controls | Changes work practices to cut how long, how often or how intensely workers are exposed | Training, job rotation, adequate rest breaks, limiting access to hazardous areas or machinery, slower line speeds |
| 5. Personal protective equipment (PPE) | Worn by workers to reduce exposure | Gloves, safety glasses, hearing protection, hard hats, respirators |
The top three work without much human effort, which is why they are more effective. Administrative controls and PPE can reduce exposure too, but they require significant, ongoing effort from workers and supervisors.
Getting the most from each level
Elimination and substitution are hardest to add to an existing process, and simplest and cheapest at the design stage — or when choosing new equipment or procedures. NIOSH's Prevention through Design approach builds prevention into equipment, tools, operations and spaces from the start. A substitute should be checked for new risks, including how it combines with other agents in the workplace; a good one reduces harm without creating new hazards.
The best engineering controls are part of the original design, stop the hazard at its source, can't be tampered with, need little effort from users, and don't get in the way of the work. They may cost more up front than administrative controls or PPE, but long-term costs tend to be lower, especially when they protect many workers, and they can save money elsewhere.
PPE should not be relied on alone when other effective options exist: it works only when used correctly and consistently, and though it may seem cheap, it can grow costly over time for many workers. Employers must provide PPE while other controls are being developed, when other controls can't reduce exposure enough, or when PPE is the only option — and should run a PPE program covering hazard assessment, selection and use, inspection and replacement, training, and ongoing monitoring.
Administrative controls and PPE are useful while higher-level controls are being put in place, and are often used in existing processes where hazards aren't well controlled.
Train and evaluate
Whatever controls are chosen, employers should train workers and supervisors to use them properly, and evaluate them regularly to confirm they are cutting exposure and to find improvements.
Sources
Based on "About Hierarchy of Controls," National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention; a work of the United States government in the public domain. See also NIOSH's Engineering Controls Database.
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