Exposure monitoring is no longer a one-off activity to demonstrate compliance with exposure standards but becomes a core input to assessing risk at work. The exposure standards for many workplace hazards have decreased in recent years. In addition, silica rules have been rewritten. Furthermore, there is an increase in the type and quality of evidence required to demonstrate that effective controls are in place at work to prevent harm to health from exposure to workplace hazards.
Regulatory and legal pressure has changed the evidentiary bar
Historically, visible dust control by means of engineering measures has been considered to be an adequate method for controlling dust at work. However, with the prohibition of use of Engineered Stone in some jurisdictions and the lower exposure standard for respirable crystalline silica in others, historic practices are being exposed to new exposure limits. Other dusts such as welding fume, diesel particulate matter and respirable coal dust are gaining increasing attention in relation to their respective exposure limits and the associated health effects.
There is also a greater burden of proof for matters in issue in prosecution and common law actions than there used to be. Thus, qualitative judgments in risk assessments are insufficient as proof of the matters dealt with in the assessment. Personal sampling data is stronger evidence than risk assessments based upon qualitative judgments alone. This is also the approach of the principal insurers and principal contractors in the prequalified contractor tender process.
Latency is the commercial risk
Noise induced hearing loss, occupational asthma, silicosis, solvent related neurological damage etc all have delayed onset symptoms that are monumentally expensive to manage and provide a useful historical record of past exposure that can be correlated with past exposure monitoring records.
Designing a sampling strategy that produces defensible data
One sample on a quiet day does not provide enough information about exposure of others working on busier shifts. It is the top end of the exposure distribution that carries health risk.
A workable strategy involves several deliberate steps.
- Define similar exposure groups based on task, agent and control regime, not on job title or payroll classification.
- Collect enough samples per group to estimate variability, generally six or more, and spread them across shifts, seasons and production rates.
- Sample the worst realistic case as well as routine conditions, and record what was happening during each sample.
- Compare results against the exposure standard using a statistical approach such as the 95th percentile, rather than a simple average.
- Reassess whenever a process, material, ventilation system or work pattern changes.
Where professional assessment adds value
This interpretation step of risk assessment exposure monitoring information can provide poor information if the sampling design of the information has not been of appropriate quality. In such cases, cost-effective instrument hire and quality NATA accredited laboratory assessment can provide all the numbers that are required. However, quality information can only be extracted from numbers with appropriate experience. This is why engaging a certified occupational hygienist for this type of workplace exposure monitoring is worth the cost. In addition to individual exposures, mixed exposures of solvents and irritants can act to additively cause a person’s limit to be exceeded even though each individual exposure is less than the person’s limit for exposure.
Matching the method to the hazard
It is not sensible to treat all exposure monitoring data as if it were the same. Different agents require different equipment, different averaging times and different ways of interpreting results.
| Hazard | Typical method | Averaging basis | Key design pitfall |
| Respirable dust and silica | Cyclone with gravimetric filter, XRD analysis | Full shift, eight hour TWA | Undersized sample mass below detection limit |
| Volatile organics | Sorbent tube or passive badge | Shift plus short term peaks | Breakthrough on high concentration tasks |
| Noise | Personal dosimetry and area sound level survey | Eight hour LAeq plus peak | Dosimeter contamination from shouting or knocks |
| Welding fume and metals | Inhalable sampler inside the helmet | Shift TWA per metal | Sampling outside the helmet, overstating exposure |
| Hand arm vibration | Triaxial accelerometer on the tool | Daily A(8) exposure | Trigger time estimated rather than measured |
Converting results into control decisions
Whether the individual results even exceed ½ the exposure standard or not, actionable data does trigger some kind of action and further investigation of the workplace exposure.
Useful actions that monitoring can justify include
- Quantifying the performance of local exhaust ventilation before and after modification, which builds a business case for capital spend.
- Setting respirator protection factors against measured concentrations rather than assumed worst case.
- Removing unnecessary controls where data shows exposure is genuinely low, freeing budget for higher risk tasks.
- Targeting health surveillance at the groups the data identifies, rather than applying it uniformly.
Closing the loop with workers
Individual results from exposure monitoring need to be communicated to individuals sampled with an explanation of the results and necessary controls to protect their health. Information from monitoring programs, including results, should be stored in safety documents. However, this information loses critical operational information on how samples were taken and validated for information.
Common failure points worth auditing
Take your occupational hygiene program team through the following to identify areas of your program that are NOT being implemented, Are all exposure groups currently included in your program still relevant? Are 15 minute average personal sampling limits as well as 8 hour time-weighted averages for each sample being taken? Is the frequency of monitoring sufficient and is it being recorded with a justification for that frequency? Are all workers covered by the main company as well as contractors and their employees and labour hire workers being monitored for potential exposures?
