A barrier can be present without performing its protective function. For each important control, distinguish the fact that it has been installed from evidence that it is effective during the work that creates the risk.
Write down its protective function
Be specific about what the control prevents or reduces. "Ventilation provided" is an equipment statement. "Capture the contaminant before it reaches the breathing zone during dispensing" describes the intended function. The second statement supports a more useful verification plan.
The NIOSH hierarchy distinguishes engineering measures from administrative controls and personal protective equipment. It also emphasises evaluating controls over time. [1]
Name the conditions it depends on
Identify assumptions such as the position of a hood, the state of an interlock, access to isolation points or the availability of a relief worker. Some controls depend on other controls, so apparent layers may not be independent.
A practical review can ask what happens at the busiest part of the shift, during maintenance and after a power interruption. These questions help define the test; they are not a substitute for a competent technical examination.
Look for evidence at the right level
Inspection can establish condition. A function test can show that a component operates. Exposure measurements or task observation may be needed to judge what happens in use. The appropriate evidence depends on the hazard and control.
For local exhaust ventilation, start with the design intent and relevant HSE guidance rather than relying only on a photograph of the installed system. [2]
Define a response to failure
Give the person doing the check a clear next step when a criterion is not met. An unresolved defect should not disappear into a dashboard. Record responsibility, interim arrangements and closure evidence.
Use the control-review worksheet in the toolkit to document the conversation. It deliberately does not produce a compliance score or a declaration that work is safe.
Sources & context
- NIOSH: Hierarchy of Controls CDC / NIOSH · United States
- HSE: Local exhaust ventilation Health and Safety Executive · Great Britain
Source-linked editorial material, prepared 2026-09-05; updated 2026-09-05. Prepared with AI assistance. Not independently peer-reviewed. Sources and legal requirements can change. The linked organisations do not endorse this publication. Our editorial approach.
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What evidence do you use to distinguish a control that is present from one that is effective?
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