US Dept of Labor

Occupational Safety & Health AdministrationWe Can Help

Evaluating Surface Contamination at Hazardous Waste Sites: Surface contamination sampling is a vital element of an effective employee monitoring program

Surface contamination sampling is a vital element
of an effective employee monitoring program.


This article is posted with permission of Stevens Publishing Corp. It appeared in "Occupational Health & Safety" Vol. 65 No. 1 January 1996.

As the health and safety officer for a hazardous waste site, how do you know that your efforts to contain contamination are working or that the personal protective equipment (PPE) chosen for workers is protecting them from exposure to site contaminants? How do you determine whether your decontamination procedures are effective, whether your housekeeping procedures are sufficient, and whether existing work zone boundaries are appropriate? If the corporate safety and health manager or an OSHA inspector arrived today, how would you demonstrate that you have evaluated the effectiveness of these aspects of your health and safety program in accordance with HAZWOPER, specifically 29 CFR 910.120 (b)(4)(iv)?1

Surface contamination sampling--often overlooked in the design of exposure assessment programs at hazardous waste sites--is one answer to each of these questions. The results of surface contamination sampling on decontaminated items or in a clean zone can be used to document that site health and safety controls are effective or, alternatively, that they are not working as expected and need modification. Similarly, sampling for surface contamination on the inner surface of PPE is an effective way to test its adequacy in preventing dermal exposure.

Surface contamination sampling is a vital element of an effective employee monitoring program, especially where dermal contamination can be a significant route of exposure through absorption or ingestion. Even when air monitoring results indicate that airborne levels of contaminants are within acceptable limits, surface contamination sampling may be advisable if skin contact with hazardous materials is possible and could contribute to overall exposure.

Sampling and Analytical Methods

Standard surface contamination sampling involves wiping a surface with a dry or wetted sampling filter and analyzing the filter contents. Small pieces of equipment, tools, PPE, or workers' skin can also be evaluated by "washing" the item and analyzing the wash liquid (see "Guidance from OSHA's Technical Manual: Standard Wipe Sampling Techniques," page 48). Alternatively, the presence of some contaminants can be evaluated instantly by touching or wiping the surface or object with direct-reading media, such as pH sticks or colorimetric pads, or by using direct reading equipment, such as mercury sniffers or radiation meters, that detect the presence of volatile substances or ionizing radiation on a contaminated surface.

Chemical analysis of standard surface contamination samples resembles analysis of other types of industrial hygiene and environmental samples. Filters used in surface sampling are typically analyzed in an on-site or off-site laboratory, whereas direct-reading detection media and equipment provide results without laboratory analysis.

Immunoassay test kits, which work like home pregnancy tests, represent a newer alternative to conventional wipe sampling technology. Collecting surface samples for immunoassay analysis is similar to standard wipe sampling, but immunoassay analysis is done very quickly on site, saving considerable time and money. Immunoassay analytical procedures require limited training and basic skills, such as the use of chemical reagents. Existing test kits offer sensitivities in the parts per million or parts per billion range but are currently available for only a limited number of contaminants (see "New Immunoassay Analytical Methods," page 49). Immunoassay kits for a wider range of substances should become available in the near future as demand increases.

Interpreting Sample Results

Results of surface contamination sampling are reported in several ways. Laboratory and immunoassay results may be reported quantitatively as the total amount of contaminant collected (in micrograms or milligrams) or as the amount of contaminant per area sampled (micrograms or milligrams per square centimeter). Direct-reading instruments do not lend themselves to quantification of contaminant levels, but they can be used simply to detect the presence or absence of a contaminant on the sampled surface. In either case, the surface contamination values do not represent airborne exposure levels.

OSHA has not established surface contamination limits. Therefore, these sampling results must be interpreted on a case-by-case or site-specific basis to evaluate the effectiveness of contaminant control measures and PPE programs.

Surface sampling results should be interpreted against objective criteria established by the employer for determining cleanliness. To establish these criteria, the employer may consider such factors as toxicity, the extent to which the contaminant occurs naturally (i.e., consideration of background levels), the environmental target levels to be achieved from site remediation, and the ability of sampling and analytical methods to quantify contaminant levels.

The remedial investigation/feasibility study for the project or the site work plan may contain information about environmental background or remediation target levels. The safety and health plan should document criteria for interpreting surface sampling results and site-specific quantitative surface contamination limits established by site safety and health management.

Incorporating Surface Contamination Sampling Into The Site Monitoring Program

Incorporating surface contamination sampling into the monitoring program enables safety and health managers to collect information that air monitoring alone cannot provide Indeed, where skin may come in contact with hazardous substances, surface sampling is the only way--aside from biological monitoring--to determine the potential contribution of surface contamination to an employee's total exposure. The results of this type of sampling can affect the job hazard analysis, PPE selection, and employee training. Surface contamination sampling also enables employers to monitor the migration of contaminants into clean areas and to modify zone boundaries if necessary, in accordance with 29 CFR 1910.(d)(2), which requires that the site control program "shall be modified as necessary as new information becomes available." Finally, surface sampling enables the employer to assess and document the adequacy of specific aspects of the safety and health plan, such as decontamination procedures and PPE selection, in accordance with 1910.120(b)(4)(iv).

The surface sampling program should be part of the written safety and health plan. Similar to an air monitoring program, the surface sampling program should describe the sampling methods to be used, the frequency and location of sampling, criteria for interpreting sampling results, and requirements for re-sampling if corrective action is necessary. The program should also include site-specific methods for removing surface contamination detected on surfaces presumed to be clean.

The appropriate frequency of surface contamination sampling depends on the type of samples being collected and prior sampling results. For example, if equipment decontamination procedures prove effective during initial evaluation, intermittent surface sampling is sufficient to ensure ongoing effectiveness of these procedures. More frequent testing may be necessary, however, if earlier results indicate that existing decontamination procedures are insufficient or if gradual chemical permeation of PPE is possible.

Zone boundaries should be monitored intermittently throughout the life of a project, unless there is reason to believe that contaminants cannot migrate across zone boundaries and earlier test results indicate appropriate zone designations. In work areas such as administrative offices that are regularly used by employees considered to be unexposed, periodic surface sampling should be conducted. This monitoring should be more frequent if activities change or prior sample results suggest a problem.

Of course, where surface contamination sampling is conducted, affected employees must be notified of the results, in accordance with OSHA's requirements for employee access to exposure and medical records, 29 CFR 1910.20. At the conclusion of project activities, final surface contamination sampling can be used to verify that all equipment and personnel gear that will be taken off-site--and perhaps reused at another site--are effectively decontaminated.

The Benefits of Evaluating Surface Contamination

Surface contamination sampling improves site characterization throughout a project and allows better decision-making with the increased level of information. The effectiveness of many safety and health procedures can be evaluated with surface sampling. When effective procedures are used and their performance is documented, potential liabilities from worker exposure or noncompliance with HAZWOPER requirements are reduced. Surface contamination sampling results may point to the absence of a hazard and justify a downgrade in PPE or other control procedures.

Direct-reading media, by providing immediate and visual evidence of surface contamination, can serve as an effective training tool to improve worker compliance with safety and health procedures. Current sampling techniques are simple, and new analytical methods offer the possibility of inexpensive, quantitative, real-time results. Remedial project managers who want to improve the characterization of safety and health hazards and ensure that their worker protection program is cost-effective will incorporate surface contamination sampling into their safety and health programs.

Nina Baird is an occupational safety and health consultant in Silver Spring, Md. Earl Cook, CIH, is a senior industrial hygienist with the Occupational Safety and Health Administration's Health Response Team. William Perry, CIH, is a health scientist with the Occupational Safety and Health Administration's Directorate of Health Standards.

The opinions, findings, and conclusions presented in this article are not necessarily those of the Occupational Safety and Health Administration. Any mention of products or materials does not imply endorsement by OSHA.

New Immunoassay Analytical Methods

Using technology similar to that used in drug screening, blood typing, and home pregnancy tests, immunoassay analysis for environmental contaminants is a promising development. Immunoassay test kits are generally used for screening purposes, but their levels of sensitivity and quantification are sufficient for most surface contamination sampling.

Kits currently marketed for surface contamination sampling are limited to PCB analysis, but the range of substances detectable by this method should expand rapidly in the next few years. A wider range of contaminants-- BTEX, PAHs, TNT, pentachlorophenol, and several pesticides and herbicides--can be analyzed with soil and water immunoassay test kits that have potential utility for health and safety sampling. For example, contaminated PPE and small equipment can be "washed" in a sealed container and the wash liquid can be analyzed with a water sample immunoassay test kit. Similarly, some contaminated surfaces can be evaluated with soil sample kits; contaminated concrete, for example, can be ground into mortar and analyzed using an immunoassay soil sample test.

Immunoassay results can be obtained in an hour or less. Current costs per sample are generally less than $30 (even less when analyzing a larger number of samples), although the total cost may be higher if a spectrophotometer or other analytical equipment must be purchased or rented. Use of immunoassay test kits is consistent with 29 CFR 1910.120(o), which contains HAZWOPER requirements for the introduction of effective new technologies and equipment for improved employee protection.

The following companies produce immunoassay kits that might be adaptable for surface contamination sampling: EM Science (800-222-0342), Ensys Inc. (919-941-5509), Millipore (800-225-1380), and Ohmicron (800-544-8881). For other potential sources of these kits, check with your sampling equipment supplier.

Superfund site audits conducted from 1992 to 1995 by the EPA/Labor Superfund Health and Safety Task Force led to the development of this article. Information about common safety and health deficiencies observed by the audit team is available in a report titled "Summary Report on OSHA Inspections Conducted at Superfund Incinerator Sites." Copies of this report can be obtained from the OSHA Publications Office, U.S. Department of Labor, P.O. Box 37535, Washington, D.C. 20013-7535, or by calling 202-219-4667 or faxing to 202-219-9266.

Is Worker PPE Performing As Anticipated?

If dermal absorption or contamination is a potential hazard on your site, the effectiveness of site PPE in preventing dermal exposure should be evaluated.

As workers exit the exclusion zone, the inner surfaces of their gloves and the sleeves or collar of their PPE can be sampled to detect permeation of contaminants. In some instances, the workers' skin can be sampled directly, although caution is necessary in using this technique. Direct skin sampling should not be done for substances that are irritants, cause dermatitis or contact sensitization, are easily absorbed by the skin, or are corrosive.

Skin, PPE, or surfaces that contact food or tobacco should be analyzed using the item wash method or should be wiped with a filter that is dry or wetted only with distilled water, not with organic solvents, PPE that is decontaminated and reused on site should occasionally be reevaluated, since chemical permeation may occur over time.

For some types of contaminants, colorimetric patches that adhere to the skin or to inner layers of gloves or clothing are available. These patches change color when chemical breakthrough occurs. Contact your sampling equipment supplier or the OSHA Salt Lake Technical Center Analytical Laboratory (801-487-0680) for more information about PPE sampling methods.

Guidance from OSHA's Technical Manual: Standard Wipe Sampling Techniques

For Standard wipe sampling, a glass filter or a paper filter is generally used for a sample collection. Through a template with an opening of known size (100 cm2is standard), the surface to be sampled is "wiped" with the filter paper, using maximum pressure and moving in concentric squares from the outside to the inside of the sampling area. The filter is then folded with the exposed side in, placed in a sampling vial, and sent to a laboratory for analysis.

The type of filter chosen depends on the contaminant and the analytical method used in the laboratory, OSHA's Chemical Information Manual or your analytical laboratory can provide chemical-specific guidance about wipe sampling methods.

General guidelines for surface contamination sampling include the following:

  • Wear clean gloves for each sample.
  • Use gloves that are disposable, impervious, and non-powdered.
  • Do not take direct skin wipes for materials with high skin absorption. Instead, sample surfaces that might contact the skin, such as the inside surfaces of protective gear or the outside surfaces of equipment, tools, tabletops, and the like. Alternatively, rinse the skin with water and analyze the rinse water (i.e., item wash method; see "Is Worker PPE Performing As Anticipated?" page 50, for more information about evaluating contamination on the skin's surface).
  • consider wetting the sampling filter with distilled water or other solvent to improve collection. The moistening agent can help dissolve the contaminant being sampled and should be chosen accordingly. For example, collection of materials with low solubility, such as PNAs or naphthalene, would be hampered by using water as a moistening agent, whereas toluene or xylene might improve collection.
  • Do not use organic solvents as a moistening agent when sampling surfaces that contact the skin, food, or tobacco products. Use distilled or deionized water as a moistening agent or a dry filter, or use the item wash method described above. Due to their volatile nature, most organic solvents are not suitable for wipe sampling.

1Inspections shall be conducted by the site safety and health supervisor or , in the absence of that individual, another individual who is knowledgeable in occupational safety and health, acting on behalf of the employer as necessary to determine the effectiveness of the site safety and health plan. Any deficiencies in the effectiveness of the site safety and health plan shall be corrected by the employer.

Back to Top

Thank You for Visiting Our Website

You are exiting the Department of Labor's Web server.

The Department of Labor does not endorse, takes no responsibility for, and exercises no control over the linked organization or its views, or contents, nor does it vouch for the accuracy or accessibility of the information contained on the destination server. The Department of Labor also cannot authorize the use of copyrighted materials contained in linked Web sites. Users must request such authorization from the sponsor of the linked Web site. Thank you for visiting our site. Please click the button below to continue.