Chemical Risk Assessment Explained: From Hazard to Control Measures

Risk assessment is a legal requirement under the EU Framework Directive (89/391/EEC) and its Chemical Agents Directive (98/24/EC). But what does a chemical risk assessment actually involve, and how do you interpret the results?

Hazard vs. Risk

These terms are often confused but mean different things:

- Hazard is the intrinsic ability of a substance to cause harm. Concentrated sulfuric acid is always hazardous — this doesn't change based on how you use it. - Risk is the likelihood that the hazard will actually cause harm in your specific situation. Using 5 mL of sulfuric acid in a fume hood with gloves is a very different risk level than handling 200 liters in an open tank.

Risk = Hazard × Exposure. A highly hazardous substance with minimal exposure can present a lower risk than a moderately hazardous substance with extensive exposure.

Qualitative Risk Assessment (Tier 1)

Tier 1 assessment uses categorical scales rather than precise measurements. This approach uses a control-banding matrix based on hazard classification, physical state, and exposure conditions — suitable for most workplace chemical exposures.

### Inhalation Risk Model

The inhalation model evaluates the risk of harm from breathing in a substance. It considers: - Hazard level (derived from H-statements in the SDS) - Physical state (gas, liquid, solid — affects how easily the substance becomes airborne) - Volatility/dustiness (for liquids: vapor pressure and boiling point; for solids: dust-forming potential) - Quantity used (small, medium, large amounts) - Exposure duration (brief, intermittent, continuous)

### Dermal Risk Model

The dermal model evaluates skin contact risk: - Skin hazard level (based on H-statements related to skin effects) - Contact area (fingertips, hands, forearms, larger body area) - Contact duration (seconds, minutes, hours) - Physical state (liquids and dissolved substances penetrate skin more readily)

### Fire & Explosion Risk Model

The fire model evaluates ignition and explosion risk: - Fire hazard level (from H-statements: H220-H232, H241-H242, H250-H252, H260-H261, H270-H272) - Physical state (gases and volatile liquids present higher risk) - Exposure potential (storage conditions, ignition sources, ventilation)

The four risk levels

Each model produces a risk rating from low to very high:

- Low: General ventilation and standard containment are sufficient. - Moderate: Local exhaust ventilation (LEV) at the point of emission; ensure adequate general ventilation. - High: Enclosed handling — fume cupboards, glove boxes, or closed systems with integrated exhaust. - Very high: Fully enclosed systems; mandatory expert occupational hygiene review. Strongly consider substitution.

From risk level to action

The risk level determines which control measures are appropriate. Following the hierarchy of controls: elimination > substitution > engineering controls > administrative controls > PPE. A very high outcome should trigger a review of whether a safer alternative exists before investing in specialist engineering controls.