What Is a COSHH Risk Assessment? The Substance-by-Substance Method

The duty, and the unit of the assessment

The Control of Substances Hazardous to Health Regulations 2002 require the employer to assess the exposure to the hazardous substances at work, and to take the control measures the assessment points to. The assessment is a risk assessment — the same logic as the general one — but the unit is the substance, not the site. One assessment per substance, per area, per group exposed: the solvent in the workshop is a different assessment from the same solvent in the lab, because the exposure and the group are different.

The assessment starts with the data source: the Safety Data Sheet (SDS), the 16-section document the supplier provides, and the label. The SDS tells you what the substance is — the hazards, the physical properties, the first aid, the spill response — and the assessment turns that data into the site document: the exposure at your site, the group exposed, the controls in place, the score, the review date. The COSHH data sheet is the site version of the SDS, and the two are the chemical record.

The register is the portfolio. Every significant substance on the site is a line in the COSHH register: the substance, the CAS number, the area, the main control, the last review, the next review. The register is the document the inspector asks for first, and the health surveillance hangs off it — the substance that is not in the register is the substance that is not assessed.

What the assessment covers: the exposure

The exposure is the heart of the COSHH assessment, and it has three questions. The route: how does the substance reach the person — inhalation (the dust, the mist, the vapour, the fume), skin contact, the eyes, ingestion? The route sets the control: the vapour is the ventilation and the respiratory, the skin is the glove and the washing, the dust is the wet method and the extraction.

The group: who is exposed, and for how long — the operator at the bench, the cleaner who comes through, the maintenance technician who opens the tank? The frequency and the duration set the likelihood: the daily exposure is a different risk from the weekly one, and the group of three is a different exposure from the one.

The amount: the concentration, the volume, the temperature, the state — the 99% solvent is a different exposure from the 10% solution, and the hot process is a different vapour from the cold one. The three questions — the route, the group, the amount — are the exposure, and the exposure is what the score is built from.

The hierarchy of controls, in the chemical order

The controls go in the hierarchy order, and the chemical order is fixed: eliminate the substance where you can — the task is not done, the substance is not used. Substitute — the less hazardous substance, the water-based for the solvent, the paste for the powder. Engineering — the local exhaust, the enclosure, the ventilation, the closed system. Administrative — the procedure, the training, the rotation, the monitoring. PPE — the last line, the glove, the respirator, the suit: the control that fails when it is forgotten.

The order is the point, and the inspector reads it in that order. The assessment that puts the respirator first and the ventilation last has the hierarchy reversed — the last line written first, and the control that fails when it is forgotten written as the first control. The substitution that removes the substance is the control the rest of the hierarchy exists because: the assessment that finds the substitution and does not take it has the duty, and the record, the same.

The pre-control score is what is there now; the post-control score is what the control moves it to. Write both — the residual is what the review reads, and the ALARP argument is the post-control, written down per substance.

Worked example: the paint-thinning task

A paint-thinning task at the bench, assessed per substance, scored before and after.

The pre-control 9 is the medium that needs the ALARP argument; the post-control 4 is the residual the review reads. The hierarchy did the work — the exhaust is the engineering control that moved the likelihood, and the gloves are the PPE that is the last line, written last. The register line carries the main control and the review date, and the health surveillance hangs off the line: the skin check, the breathing check, the date. The substance is assessed, the exposure is controlled, and the register is the record.

The register, and the review

The register is the site view of the assessment: one line per significant substance, with the substance, the CAS number, the area, the main control, the last review and the next review. The register is the document that keeps the chemical side honest over the year — the substance that arrives with the new product is the line that is added, and the substance that leaves is the line that is retired, with the date.

The review is per substance, at least every two years, and on the event: the incident, the change to the substance, the change to the process. The review checks the three things — is the exposure still the one assessed (the route, the group, the amount), is the control still in place (the exhaust, still running?), is the residual still acceptable (the post-control, still the case?). The review that finds the control has gone, or the exposure has changed, is the review that starts the re-assessment.

The health surveillance is the line that proves the control worked: the skin check for the dermatitis, the breathing check for the asthma, the date. The surveillance is not the assessment — it is the check on the assessment, the evidence that the exposure the control moved is the exposure the worker is actually in. The assessment, the register and the surveillance are the chemical record, in the three documents the duty needs.

The mistakes that fail the chemical assessment

The COSHH assessment that fails the review fails for a small set of repeatable reasons. The substance not in the register: the product that arrived with the new order, and the register that does not see it — the line that is not written is the substance that is not assessed. The exposure not assessed: the route, the group, the amount — the assessment that names the substance and stops there, without the exposure, is the label, not the assessment.

The hierarchy reversed: the PPE first, the engineering last — the last line written first. The SDS not read: the assessment written from the memory, not the 16 sections — the hazard that the SDS names and the assessment does not. The review not done: the two years pass, and the register that is not reviewed is the register that is decoration. The surveillance not hung off the line: the check that is not tied to the substance is the check that does not prove the control.

The chemical assessment is the substance, the exposure, the hierarchy, the score and the register — per substance, per area, per group. Where the substance is the significant one, the template is the preparation and the competent person is the sign-off: the chemical record, in the documents the duty needs.