The majority of serious occupational disease causing hazards have no near miss report associated with them. Reports of incidents where workers have fallen ill after exposure to a substance over a long period of time are non-existent. Information gathered from injury reports is limited to the energy released at the time of the accident or incident. In contrast, health hazards release no energy and can cause serious harm over a long period of time.
Why routine inspections miss chronic exposures
Your existing inspections for visible risk (such as for guarding, housekeeping, work at height, traffic management, etc.) will find most of these potential problems before they cause an accident or injury. Workplaces with airborne contaminants (such as toxic or ototoxic gases and fumes), respirable solid particles (such as respirable crystalline silica), and bioaerosols can’t be found by a normal walkthrough inspection using a checklist to see if there is any dust about.
Signals already sitting in your systems
Before embarking on any sampling, find out if there are any existing data sources that have identified exposures that the inspections have not found.
- Chemical register entries with no corresponding risk assessment, or safety data sheets more than five years old.
- Maintenance records showing repeated repairs to local exhaust ventilation, or fans running at reduced capacity.
- Purchasing data for respiratory protection that has climbed without a documented change in task.
- Audiometry results showing early high frequency loss clustered in one work group.
- Non-routine work such as breakdowns, confined space entry and shutdowns, where short tasks generate the highest exposures.
Define exposure groups before you sample
When developing an exposure monitoring program, remember that random sampling will only provide expensive data to answer a question that you have not thought about. Begin with a qualitative exposure assessment that outlines all of the tasks, agents, duration and controls. Then group workers by similar exposure and develop the monitoring strategy based upon the work that they actually perform, as opposed to their departmental location.
Getting the groups right
Don’t assume a given position is in a given group, test the boundaries. Highly variable samples can form a number of groups, but ideally each group should have the highest exposure in the group represented. Very wide groups ‘average out’ lower exposure workers to appear to be OK but are not.
Matching the monitoring method to the agent
Various sampling methods and corresponding techniques and sampling durations are needed for the various classes of hazards. The most common methods and what you can achieve with them are listed in the table below.
| Hazard | Typical monitoring approach | What it resolves | Common pitfall |
| Respirable crystalline silica | Personal cyclone sampler, gravimetric plus XRD or FTIR analysis | Eight hour time weighted exposure against the 0.05 mg/m³ standard | Sampling only routine work and omitting clean-up tasks |
| Welding fume and metals | In-helmet or breathing zone filter, ICP analysis | Individual metal fractions including manganese and hexavalent chromium | Treating total fume as a proxy for specific metals |
| Solvents and vapours | Sorbent tube or passive badge, GC-MS | Mixed exposures and short term peaks | Ignoring additive effects across a mixture |
| Noise | Personal dosimetry plus octave band analysis | Daily dose, peak levels and frequency content for control design | Relying on area sound level readings alone |
| Biological agents | Bioaerosol sampling, surface swabs, water sampling | Legionella, mould and endotoxin sources | Sampling without a hypothesis about the source |
Where specialist judgement earns its keep
Determine a method and establish a sampling strategy (including flow rates, blanks, and laboratory confirmation) to answer a specific question or determine if certain exposure limits are being met. Where that strategy needs to stand up to scrutiny, it is worth engaging an occupational hygiene consultancy, and a Certified Industrial Hygienist (CIH) can assist in establishing these necessary components.
Reading results properly
Once a sample has been taken and sent off to a laboratory for analysis, the results of a single sample must be treated with a healthy dose of scepticism. The results of a single sample will rarely provide sufficient information to come to a conclusion about the exposure of a worker to a substance. Exposures to most substances are log-normally distributed, and therefore, the upper 95% confidence limit of the results must be compared against the standard to provide some assurance that exposures are below the acceptable limit.
Setting action levels
The threshold for most programs is set at half the exposure standard (i.e. At half the exposure limit, unless specified otherwise) as there can be day-to-day variation in exposure. For highly sensitising or carcinogenic substances or where a standard is currently under review, exposure limits may be set at a lower internal trigger. Ensure that the decision-making process is recorded in case staff change over time.
Converting findings into lasting control
It must matter. Use the findings to drive prioritisation of eliminate and substitute followed by appropriate engineering, administrative and personal protective equipment measures, in that order.
- Re-monitor after any control change to confirm the reduction, rather than assuming it.
- Schedule ventilation performance testing at fixed intervals and record face velocities over time.
- Align health monitoring to the agents actually confirmed by sampling.
- Review exposure groups whenever process, product or roster changes occur.
Many occupational exposure monitoring programs fail because of the perception that the assessment is merely an occasional compliance check. It is not. Exposure data should be considered as another production, maintenance or quality operational metric and viewed with the same discipline.
