The hierarchy of control is one of the most important questions in any safety officer interview, and one of the most useful tools on site. Whenever there is a hazard, you apply these five controls in order, starting from the most effective one.
The 5 levels of the hierarchy of control
- Elimination: remove the hazard completely.
- Substitution: replace the hazard with something less dangerous.
- Engineering controls: isolate people from the hazard with physical measures.
- Administrative controls: change the way people work (procedures, permits, training, signs, work location).
- PPE (Personal Protective Equipment): protect the worker’s body as the last line of defence.
The controls at the top are the most effective because they deal with the hazard itself. The ones at the bottom depend on people following rules and wearing equipment correctly, so they are less reliable.
1. Elimination
Get rid of the hazard so it no longer exists. For example, if loose material is lying at a height where it can fall, remove it from there completely. If the hazard is gone, nobody can be hurt by it.
2. Substitution
If you cannot remove the hazard, replace it with something that carries less risk. For example, use a less hazardous chemical, a lighter tool, or carry out the work at ground level instead of at height, so a high-risk situation becomes a low-risk one.
3. Engineering controls
Put a physical barrier between people and the hazard. For example, install barricades, guard rails or toe boards at the edges so that objects cannot fall, or fit machine guards on rotating parts.
4. Administrative controls
Here management changes how or where the work is done. For example, moving the activity to a safer location, issuing a permit to work, restricting access to the area, rotating workers, giving a toolbox talk or putting up warning signs.
5. PPE: the last line of defence
If a risk is still left, PPE protects the worker. For example, during high-risk work where something could fall from above, workers below wear helmets, and a protective layer or net is installed. If a hammer falls, it hits the helmet instead of the worker’s head.
How to answer in an interview
Name all five levels in the correct order, explain each in one line with a site example, and mention that PPE is always the last option, not the first. Interviewers often follow up with a scenario, so practice applying the hierarchy to activities like work at height, lifting and excavation.
Test yourself: take the Hierarchy of Control quiz.