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Safeguard OSH Solutions - Thomson Reuters

Safeguard OSH Solutions - Thomson Reuters



Safeguard Magazine

Follow your nose

Before you spend money on air quality monitoring, says IAN BARTLETT, learn all you can with your senses.

Good occupational hygiene is about controlling exposures – but before you can control an exposure you need to know what it is that needs controlling.

For occupational hygienists the three watch words are Recognise, Evaluate, and Control – or, in other words, hazard identification, risk assessment, and risk management.

Many people think the first step means sampling, but there are things to be considered before you embark on a sampling regime.

To start with, sampling is not something that should be done in isolation, just for its own sake. If you are doing it, it has to say something about the control you have over the substance you are sampling for.

There are several types of sampling you can do – initial appraisals, basic surveys, detailed surveys, and routine surveys – and all these can be quite different from one another.

What should you use for our initial appraisal? Your eyes, ears, and nose. In some circumstances your nose can be far more sensitive than any scientific instrument. It can detect parts per million, and even parts per billion or lower of some substances. It won’t tell you the exposure level, but it will tell you whether the substance is there or not.

Often a walk-through may be all that is needed for your initial survey.

Beyond the WES

Air sampling programmes are often driven by Workplace Exposure Standards, but there are lots of substances which don’t have a WES – in fact there are probably more substances that don’t have one than do.

That doesn’t mean, however, that we can’t make some projections about the levels you might not want to be exposed to. You can do lots of different types of measurement for airborne hazards – qualitative ones as well as quantitative. If a smell is unpleasant and people don’t want to be exposed to it, you probably need to do something about it.

If you think you need to carry out sampling, the first thing you need to do is set a budget. You are not going to get a sample for nothing and the equipment can be a significant cost. A basic solvent survey with ten samples, for instance, can cost around $8000. Polycyclic aromatic hydrocarbons can cost $220 per analysis, so ten samples will be $2000 plus, and dioxins can cost $2000 per sample.

You need to remember that the end goal is not the sampling itself – it’s controlling the exposure, and sometimes your eyes, ears and nose are better value indicators.

You would be better to spend the money on controls than on sampling if it’s only going to tell you what you already know.

The old routine

Then there is routine sampling. You use this to check your controls and your WES compliance, and to keep track of any problems. We don’t do much of it because it is a significant expense, and its value is to be questioned.

If you’re doing routine sampling, its efficacy must be regularly reviewed. Ask yourself: How often do I need to sample? What’s a proactive response?

If you had a factory making light bulbs, in the first production run you might run a quality control check of 10% of the production run. Once you’re up to speed this would reduce to around 5%, and eventually if everything was going well it could drop down to 2.5%.

The same goes for air sampling. Unless you identify something unexpected you can consider reducing the level of sampling over time.

The important thing with this sort of sampling is to look for patterns in the results.

Do exposure levels change between shifts? At different times of day? Over the week? Or between winter and summer? If you do find variations, look at what they mean. Are you carrying out different processes at different times?

Perhaps you have the doors open in summer, or during the day, and close them in winter, or at nights?

Sometimes, too, I come back with sampling results to show people what I’ve found and they say we don’t use that substance here. You need to think about not only the chemicals you are using, but also possible by-products of your processes, or even something that may have drifted in from next door.

Making samples meaningful

One of the problems with occupational hygiene sampling is that population sizes are often very small. There may be only 15 people in a workplace, all doing different tasks with different exposure levels.

There are formulae for determining the number of samples you need to get a reliable picture of exposure levels, but you have to use modified versions for such small groups.

The most important thing is the task – how many people are doing a particular task, and what are the exposures associated with it?

A good preliminary survey and a reasonably detailed survey will often give you the answer you need here, then you may only need two or three samples through the year to make sure things are still okay.

If you don’t do enough sampling in the initial stages, however, you won’t get useful results. If I have a bag of 22 marbles, one of which is black, and take marbles at random from a bag, the average number of samples I need to be fairly sure of getting the black one is 14.

Small workforce, large sample

In a pre-election survey, pollsters only question a percentage of the population to predict the outcome of an election.

It’s the same with sampling. To find, say, the highest exposure level, you need to take a statistically-based number of samples to be sure of getting it.

If you have a smaller workforce you need to sample a higher proportion of them – from eight workers or eight similar work tasks you will probably need to sample seven of them. But the proportion goes down as the size of the workforce increases. If you have two people doing a task, sample them both, but the more people you have doing a homogenous task, the lower the proportion of the population that needs to be sampled.

There is no point in just doing one sample. That won’t give you the answer. So if your resources are limited, ask yourself if your money would be better spent on some expert help and controls to reduce exposure rather than sampling to measure it.

IAN BARTLETT is a registered occupational hygienist who works as a consultant with Paragon Health and Safety. ian@paragonhs.co.nz

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