Occupational Health Risk Assessment (OHRA)
Qualitative screening and quantitative measurement of the health hazards your workers face
An occupational health risk assessment (OHRA) is the structured process of identifying the health hazards in a workplace, working out which groups of workers are exposed to each hazard, and rating the risk to their health so the right controls and the right monitoring can follow. It covers chemical hazards such as dusts, fumes, solvents and gases, physical hazards such as noise, vibration, heat and radiation, and biological hazards. An OHRA is carried out in two stages: a qualitative OHRA screens every hazard by observation and professional judgement, and a quantitative OHRA measures the exposures the screening could not clear. Together they decide what an occupational hygiene monitoring plan must measure, how often, and for whom.
Why an OHRA Comes Before Monitoring
The WHS Regulations require a PCBU to manage the risks to health from hazardous chemicals, noise and other health hazards, and to ensure that no worker is exposed to an airborne contaminant above its workplace exposure limit. Air monitoring is required where the PCBU is not certain on reasonable grounds that exposure is below the limit, or where monitoring is needed to work out whether there is a risk to health. An OHRA is how a PCBU reaches that certainty, or finds out that it does not have it. Without one, monitoring is either guesswork, measuring the wrong things or the wrong people, or absent where it is actually required. The assessment also records the reasoning, which is what a regulator asks for when it questions why a particular exposure was, or was not, measured.
Similar Exposure Groups
An OHRA does not assess workers one at a time. Workers are grouped into similar exposure groups (SEGs): people who do the same tasks, with the same materials and controls, for similar durations, and whose exposure can therefore be expected to be alike. A fabrication workshop might have a welding SEG, a grinding and finishing SEG, a paint-shop SEG and an office SEG. Each hazard is then assessed for each group. Defining SEGs well is the most important step in the whole process, because every later decision, from which groups need sampling to how many samples are enough, rests on it.
Qualitative vs Quantitative OHRA
Qualitative OHRA
A competent person, usually an occupational hygienist, walks through the workplace and observes each task. For every similar exposure group and hazard they rate how severe the health effect could be and how likely exposure is, using the quantity of substance handled, how often and how long the task runs, and the controls in place. The two ratings combine into a risk ranking such as low, medium or high. No samples are taken. The output is a prioritised list showing which exposures are clearly controlled and which need measuring.
Quantitative OHRA
Exposure is measured rather than estimated: personal air sampling in the worker's breathing zone, noise dosimetry, or biological monitoring where it is appropriate. Results for each similar exposure group are compared with the workplace exposure limit, and enough samples are collected to judge the group's exposure statistically rather than from a single result. A quantitative assessment is needed where the PCBU cannot be certain on reasonable grounds that exposure is below the exposure standard — the trigger for the air monitoring duty described above.
How the Two Stages Fit Together
The qualitative stage keeps monitoring focused: groups rated low with good controls are documented and reviewed, while groups rated medium or high, or where the rating is uncertain, go forward to quantitative assessment. The quantitative results then set the OHMP's sampling programme, its trigger levels and how often each group is reassessed. Both stages are repeated when processes, substances or controls change, and the WEL transition on 1 December 2026 is one such change.
What the Assessment Produces
A completed OHRA delivers a register of health hazards by SEG with a risk rating for each; a list of the exposures rated low with the controls that justify the rating; a list of the exposures that require quantitative assessment, with the contaminant, the sampling method and the exposure standard to compare against; the measured exposure results and their comparison with the workplace exposure limit for the groups that were sampled; and a set of recommendations covering controls, health monitoring where a hazard such as silica, lead, asbestos or isocyanates triggers it, and the review date. The quantitative results and the recommendations become the basis of the occupational hygiene monitoring plan.
When an OHRA Should Be Reviewed
An OHRA is a point-in-time document. It should be reviewed when a process, material or control changes, when new information about a hazard becomes available, when monitoring or health monitoring results suggest the rating was wrong, after an incident or an exposure complaint, and otherwise at the interval the assessor sets, commonly every one to three years depending on the hazards involved. The December 2026 changes to a number of workplace exposure limits are a review trigger in their own right: a group rated low against the current limit may not be low against a lower one.
Commission an OHRA
OHConnect connects you with certified occupational hygienists who carry out qualitative and quantitative occupational health risk assessments across Australia and turn the results into a monitoring plan you can act on.