- posted at 06:00PM
- August 31, 2011
- by: Bill Beadie
- Email to a Friend
As an industrial hygienist, I’m frequently asked to assess people’s exposure to hazardous chemicals. Usually, the conversation starts something like this:
“Hi. I’d like to set up some air monitoring to assess employee X’s exposure to chemical Y. September 18 would be good because we’ll be running our highest level of production, so that should be worst-case.”
The person making this request typically expects me to conduct this air monitoring and then write a report summarizing the results compared to some limit, such as an OSHA Permissible Exposure Limit (PEL). If all the results are below the limit, the report gets dropped into the file for future reference. If results are over the limit, I’m expected to make recommendations that will bring the facility back into compliance.
The person making this request probably doesn’t know that he or she already completed the most important parts of an industrial hygiene assessment. Specifically, the person had:
- Identified the goals of the assessment,
- Decided on the assessment strategy and criteria, and
- Performed a basic characterization of the workplace and identified jobs, tasks, and agents that warrant exposure monitoring.
After asking some questions, I discover that people usually want to know whether they are adequately protecting workers from overexposure to hazardous chemicals, not just the average airborne concentration of chemical Y on September 18. That allows us to start at the beginning and talk about the assessment goals and the appropriate strategies to achieve those goals.
Although good exposure assessments are somewhat sophisticated, they are not impossibly complex or astronomically expensive. Good assessments require an organized and thoughtful strategy, which, in the long run, will be more efficient and a better use of resources than simply grabbing a few air samples.
I can’t provide a “one-size-fits-all” approach for industrial hygiene projects, but the initial conversation with an industrial hygienist can be straightforward if you consider the following:
- Projects frequently include a preliminary evaluation to identify combinations of jobs, tasks, and agents that contribute to employee exposure. Developing a prioritized list of these groupings, commonly called similar exposure groups (SEGs), can provide an organized framework for efficiently planning assessments.
- Employers should strongly consider developing an exposure profile for all SEGs, even if they expect to be in compliance with established limits.
- Modeling employee exposures can be a cost-effective way to supplement or even replace traditional sampling. Although appropriate modeling requires experience, it can be a valuable tool for addressing sampling program limitations.
- Skin exposures should be carefully evaluated in many cases. Even a relatively simple qualitative assessment can provide valuable information to help protect workers.
- Assessment results should frequently be judged against the available toxicological data, not just the PELs.
- Air sampling results should be evaluated after considering the desired confidence in the conclusion.
The last bullet point about confidence in the data has inspired many interesting conversations and a fair amount of confusion. I’ll attempt to clarify the point with the analogy of quality control / quality assurance programs. Most manufacturing facilities have some process to determine whether the product meets specifications, and that process usually involves testing some percentage of the product against objective criteria (e.g., weight, volume, color, strength). Let’s take the following hypothetical example:
ACME Bolt Company specifies that all bolts must support a maximum load of 14,500 pounds. They test 2% of all bolts produced and every test shows that the bolts support between 19,500 and 20,000 pounds. In this case, the relatively small variation in results, all of which are well above the minimum specification, may justify reducing the sampling frequency.
The next week, the specification suddenly increases to 19,250 pounds. ACME is now faced with a more troubling scenario. Either they:
- Produce sturdier bolts (at significant cost) to get a comfortable safety margin,
- Hope they don’t accidentally produce any bolts that fail to meet the specification, or
- Strengthen their testing program to identify any bolts that fail to support 19,250 pounds.
In the world of industrial hygiene, it is not uncommon for management decisions to be made with absolutely no sampling data. Even assessments based on data are frequently based on fewer than ten samples. Although this may suggest that we need to collect far more samples (which may be true), it can also suggest that we should investigate ways to assess exposures without requiring incredible sampling costs. Let’s continue with our ACME Bolt Company example.…
ACME management installs some automated measuring devices on the production line. For a modest investment, they can now perform some measurements on 100% of the bolts, which allows the ACME engineers to estimate the strength of each bolt. The estimated strength is validated by additional measurements on a smaller percentage of bolts, and an even smaller percentage is sent for the full pull test. The testing program, which requires a much smaller investment than simply beefing up the bolt construction, shows that the current manufacturing practices can reliably meet the more stringent specification.
Industrial hygiene assessments can be designed like our hypothetical example. Detailed process information, screening tests, modeling, and some traditional sampling can effectively define an exposure profile in a way that recognizes uncertainty and limited resources. However, this requires expertise, organization, and a commitment to achieving the goals of a well-defined strategy. All industrial hygiene assessments should be thoughtfully designed from the very beginning in order to provide the most useful information possible.