You don't have to be a certified industrial hygienist to do personal air sampling." That's what I've told hundreds of participants in introductory industrial hygiene courses I have taught since 1994. Discussions with participants in these courses revealed that many otherwise (apparently) competent safety practitioners were intimidated by the very thought of doing any type of industrial hygiene air sampling other than perhaps evaluating a confined space prior to entry. Some participants seemed to view industrial hygiene as wizardry practiced by magicians who did mystical things to test workplace air. Others were bewildered by the seemingly endless array of gadgets and gizmos that industrial hygienists used to perform their magic and felt that they lacked the requisite skills to use such arcane hardware. Still others thought that they would incur the wrath of industrial hygienists if they encroached on their sacred turf.
I tried to demystify industrial hygiene sampling process in a logical step-by-step manner, while demonstrating typical industrial hygiene sampling equipment and providing a caveat that air sampling that required a lot of professional judgments should be left to the CIHs.
Some sampling, however, can be adequately performed by a trained technician. Perhaps the best example of this is the periodic routine sampling required by OSHA's substance-specific health standards such as lead, methylene chloride and cadmium.
The OSHA standards list permissible exposure limits (PELs) for about 600 chemicals, such as acetone, methyl ethyl ketone, toluene and ethyl alcohol, that are commonly found in the industrial environment. Although OSHA has airborne limits for these substances, the agency does not specifically require that air sampling be performed to evaluate employee exposures to most of these substances. Instead, it simply requires that employee exposures to the regulated chemicals remain below the PEL. Although the most practical way of making this determination is to perform air sampling, sampling is not mandated for the vast majority of the substances that OSHA regulates.
However, there are a handful of substances (Table I) that specifically require that air sampling be performed. Moreover, these substance-specific standards require that periodic sampling be performed on a regular basis such as monthly or quarterly. Some of the substances such as lead, cadmium and methylene chloride may be found in many workplace settings.
For example, lead and cadmium pigments are used in some industrial paints and coatings. Employees may be exposed to these substances when they perform operations such as spray painting with materials containing these pigments or when they perform welding or oxy-fuel gas cutting on metal surfaces protected by lead- or cadmium-containing coatings. Methylene chloride is a common industrial solvent and often used for paint removal and furniture stripping.
Other substances are found only in a few very specific settings. For example, coke oven emissions are found only in steel mills that have coke ovens and cotton dust is found only in facilities that process raw cotton. Ethylene oxide is a feed stock for some chemical manufacturing processes and is commonly found in hospitals, where it is used to sterilize delicate medical devices.
Since sampling to meet the requirements of substance-specific standards is routine and repetitive, it can easily be performed by someone other than a certified industrial hygienist. As a practical matter, once the person performing the sampling becomes proficient with generally accepted industrial hygiene practices such as how to calibrate the sampling equipment, how to place the equipment on employees, what field information to document and how to properly handle the samples and submit them to the laboratory, it is then just a matter of repeating those tasks without the need to make the types of professional judgments that are best left to the CIHs.
Personal Sampling Explained
The type of sampling required by OSHA's substance-specific standards is called personal breathing zone sampling. The sampling is "personal" because it evaluates an individual employee's exposure to a chemical as opposed to area sampling that measures the concentration of a substance in a given area (e.g., the amount of carbon monoxide in a warehouse where gasoline-powered forklifts are being used). Although certain inferences can be made about exposure by considering the length of time an employee is in the area, the best indicator of a person's actual exposure comes from personal sampling since the sample is collected by equipment that is actually worn by the employee during the work day.
Because the samples are collected at the employee's nose and mouth, they are called "breathing zone" samples. The breathing zone can be visualized as a hemisphere about 6 to 9 inches around the employee's face. Breathing zone samples provide the best indication of the concentration of contaminants in the air the employee is actually breathing. Two types of instruments are commonly used to do personal breathing zone sampling: passive monitors and personal sampling pumps.
Passive Monitors Passive monitors are small plastic enclosures about half the size of a pager. They are filled with a granular solid sorbent such as activated charcoal that has an affinity for organic gases and vapors. One section of the enclosure is open to the air. Organic gases and vapors in the air that pass through the opening by diffusion are adsorbed, or trapped, by the sorbent material.
At the beginning of the sampling period (for instance, at the beginning of the work shift), the monitor is placed in the employee's breathing zone by clipping it to his shirt collar. A protective cover that seals the opening in the monitor is removed, allowing air to diffuse into the monitor. The time the cover is removed is noted and the monitor remains attached to the employee throughout the work shift in essence, breathing the same air the employee breathes.
At the end of the sampling period, the cover is replaced, the monitor is removed and resealed and the time it is removed is noted. The total time the open monitor was exposed to the air is calculated by subtracting the time it was put on from the time it was taken off. A laboratory submission sheet is completed and the monitor is sent to the laboratory for analysis. The laboratory will extract the contaminant from the sorbent and use a diffusion coefficient to calculate the concentration of the gas or vapors the employee was exposed to and subsequently provide you with a written report containing that information.
Personal sampling pumps. One drawback to passive monitors is they are only able to measure gases and vapors, but many contaminants exist as particulates such as dust, metal fumes or mists. A different type of personal monitor is required for particulate sampling, but that equipment can also be used to measure gases and vapors. The sampling systems consists of two components a personal sampling pump, which is a small battery-powered vacuum pump, and a collection media, usually a filter or sorbent tube on which the substance of interest can be collected. The pump is attached to the worker's belt either behind his back or above his hip using a belt clip on the pump and the collection media, supported by a holder, is clipped to the employee's shirt collar in his breathing zone. The media holder is attached to the air inlet fitting on the pump with a short length of plastic tubing that is run behind the employee's back. The combination of pump and attached collection media is called a sampling train. When the pump is turned on, it pulls air through the collection media and contaminants in the air are trapped for subsequent laboratory analysis. Two types of media are commonly used for industrial hygiene sampling sorbent tubes and filters.
Sampling with Sorbent Tubes. Sorbent tubes are small glass tubes about a quarter inch in diameter and 2 to 4 inches long that are filled with a granular solid substance such as activated charcoal or silica gel or a proprietary substance. One end of the tube is attached to the pump with a short piece of plastic tubing. The other end is open to the environment. Air is drawn through the tube by the sampling pump and vapors in the air are trapped by the sorbent. At the end of the sampling period, the tube is removed, the open ends are covered with tight-fitting plastic protective caps and it is sent to the laboratory for analysis.
Sampling with Filters. Most industrial hygiene sampling for particulates is done using a filter that is 37mm in diameter. One exception is asbestos, which uses a 25mm diameter filter. The two most commonly used filters are made of polyvinyl chloride with a 5-micron pore size and mixed cellulose ester with a 0.8 micron pore size. The filters look like very thin plastic discs with the consistency of stiff tissue paper because the filters are so delicate. They are placed in a small plastic cassette to facilitate handling. The cassette is a cylinder about 1 inch in diameter and 2 inches long. The filter is placed on a porous support in the middle of the cassette and spans its cross-sectional area. The cylinder has openings on both ends, like the sorbent tubes. One end is connected to the pump with a length of plastic tubing. The other is open to the air. When the pump pulls air through the filter, particulates are collected on the surface of the filter in same way that the air filter in a car collects road dust. Like the sorbent tube, the filter cassette is clipped to the employee's collar in the breathing zone.
At the end of the sampling period, the openings on the ends of the cassette are sealed with a plug and the cassette is sent to the laboratory for analysis. When sampling with sorbent tubes and filters, the laboratory must be provided with the volume of air sampled which is determined from the low rate of the pump known from calibration and the duration of the sampling period. Calculations for this determination will be discussed in the next installment of this series.
Understanding OSHA's Substance-specific Health Standards
Because of minor differences that exist between each of OSHA's substance-specific standards, particularly with respect to the frequency of periodic monitoring and the point when monitoring may be discontinued, anyone interested in doing air monitoring to fulfill the regulatory requirements should carefully review the relevant standard and become intimately familiar with the exact requirements for the substance of interest.
Note that the discussion below is limited solely to requirements related to air sampling. Substance-specific standards also include detailed requirements for a plethora of other concerns such as employee training, medical surveillance, protective clothing and equipment. Some of the provisions pertaining to air sampling that are common to most of the substance-specific standards are described below but remember the exact requirements vary from substance to substance.
Acceptable exposure limits. Substance-specific standards establish a permissible exposure limit (PEL) that must not be exceeded and an action level, typically half of the PEL. Both are expressed as 8-hour time-weighted averages. The action level is a concentration that is used to establish the frequency of routine sampling and is sometimes used as a factor in determining when air monitoring may be discontinued. For example, sampling for methylene chloride may be discontinued when two consecutive measurements taken seven days apart are below the action level. Some substances such as acrylonitrile establish ceiling or short-term exposure limits that cannot be exceeded over a 15-minute period during the day.
All exposures are considered without regard to respiratory protection. In other words, if the employees being sampled are wearing respirators, the protection afforded by the respirator is not taken into account when considering the level of exposure.
Accuracy of the measurements. Substance-specific standards typically stipulate the level of accuracy that the sampling and analytical method must meet.
Initial monitoring. Initial or baseline sampling must be conducted to determine the existing level of exposure. The results of this monitoring are used to establish the frequency of periodic monitoring and may invoke other requirements of the standard, such as medical surveillance, protective equipment and written compliance plans.
Periodic monitoring. The frequency of periodic monitoring varies from substance to substance and is based on where the measured exposure is relative to the action level or PEL. The vinyl chloride standard, for example, requires monthly sampling for any employee exposed above the PEL. The benzene standard, on the other hand, requires annual sampling for employees exposed above the action level but below the PEL, and sampling every six months for any employee exposed above the PEL.
Termination of monitoring. Results of the periodic monitoring are used to establish when monitoring may be discontinued. For example, the lead and cadmium standards permit monitoring to be discontinued when two consecutive samples taken at least seven days apart are below the action level.
Additional monitoring. The standards include a provision for conducting additional monitoring whenever there has been a production process, control or personnel change, or when there is reason to suspect other change which may result in a new or additional exposure.
Employee observation of monitoring. Some standards such as butadiene specifically require that employees or their representatives be provided with an opportunity to observe the monitoring. This provision is to ensure that union representatives be afforded the opportunity to observe the sampling process.
Informing employees of monitoring results. Employees must be informed in writing of the sampling results within a prescribed time after receipt of the results from the laboratory, but the notification period varies among substances. For example, notification of the results for acrylonitrile, lead and DBCP must be provided within five days but 15 days is allowed for cadmium and benzene.
Records. Some standards dictate specific information that must be part of the employee's exposure record. For example, the coke oven emission standard stipulates that the record must contain the name, social security number and job classification of the employee and the type of respiratory protection worn, if any. Sampling records must be maintained in accordance with 29 CFR 1910.1020, "Access to Employee Exposure and Medical Records," which requires exposure records to be retained for the duration of the employee's employment plus 30 years. The standard also requires that records be made available to OSHA representatives upon request and that employees or their representative be provided a copy of their exposure record or the means to make a copy upon request.
Obtaining Training on Sampling Procedures
Although the mechanics of personal sampling can be self-taught (an excellent source of information for self-guided work is chapter one of the OSHA technical manual which can be found on the OSHA Web site, http://www.osha.govwww.osha.gov), some people may find that learning is facilitated by some formal instruction. Both the National Safety Council and the American Industrial Hygiene Association offer introductory industrial hygiene courses that include instruction on sampling. Some colleges and universities also offer short courses on air sampling. State OSHA consultation programs may also be willing to provide some hands-on training.
If you have your own sampling equipment, another option which may not occur to many people, but provides an excellent way of obtaining very practical customized instruction at relatively low cost, is to arrange for some one-on-one tutoring from a local industrial hygiene consultant in your area.
This option offers a number of significant advantages. The cost for a few hours of an industrial hygienist's time will probably be less than the cost of attending a formal course and you would also have your tutor's full attention rather than being just one other person in a large group. Perhaps the two biggest advantages of this approach are that you can receive hands-on instruction on the specific equipment you will actually be using, and that the instruction and hands-on practice can take place in the environment where you will be sampling and with some of the workers you will eventually be sampling, rather than merely practicing in an artificial classroom simulation. With a certified industrial hygienist working right next to you, you will be able to discuss at length any questions you have about calibration using the equipment in the field or handling and processing your samples.
Once you develop proficiency in the procedures, you can begin doing the periodic sampling required by the standard on your own. Many industrial hygienists probably would be delighted to share some of their knowledge and experience with an enthusiastic disciple. And establishing a regular working relationship with an industrial hygienist affords you the opportunity to discuss any other concerns you may have about such things as respirator selection, respirator fit testing or installation of a ventilation system to reduce exposure.
Table I: OSHA Substance-specific Health Standards
Substance 29 CFR 1910
Vinyl chloride: .1017
Inorganic arsenic: .1018
Coke oven emissions: .1029
Cotton dust: .1043
1,2 -Dibromo-3-chloropropane: .1044
Ethylene oxide: .1047
Methylene chloride: .1051
Contributing Editor John F. Rekus, PE, CIH, CSP, is an independent consultant. He has more than 20 years of regulatory experience and may be reached at (410) 583-7954.