Letting Surfaces Tell a Story
New Guidance from NIOSH on Surface Sampling
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Industrial hygienists consider a variety of approaches when evaluating occupational hazards. Workplace surfaces offer a wealth of information about many aspects of a workplace, including but not limited to air contamination that has settled, the potential for dermal exposure, the source of an agent that can be re-entrained, and evidence of the effectiveness of workplace controls. Sampling surfaces can provide useful information for making decisions about workplace exposures and controls. However, it is important to design a surface sampling program that provides consistent, reproducible, useful data. To do so, we must look closely at each aspect of the sampling process and make decisions about the performance requirements of the plan. THE NEED FOR GUIDANCE Depending on the agent and the workplace, few comprehensive resources are available to design surface sampling campaigns and interpret results. Sometimes workplaces are subject to regulatory requirements, but often hygienists must determine all aspects of surface sampling, using an assortment of resources. One famous example of using surface sampling results for decision-making was the evaluation of United States Postal Service buildings for reoccupancy following the release of Bacillus anthracis in 2001 and the subsequent cleanup. A few years later, the Government Accountability Office published a report calling for additional research into the development and characterization of surface sampling methods and strategies to improve confidence in negative results prior to building reoccupancy. Since then, researchers and practitioners have endeavored to characterize and standardize surface sampling methods and strategies so the data obtained can be interpreted appropriately. Increasing attention has been paid to surface sampling within occupational health and safety. In 2019, ACGIH began publishing Threshold Limit Values-Surface Limits, or TLV-SLs, to supplement air values. Recently, U.S. Pharmacopeia General Chapter <800>, Hazardous Drugs—Handling in Healthcare Settings, established surface sampling as a component of safe handling programs in healthcare facilities. Taking a broader perspective, recent research published in the Journal of Occupational and Environmental Hygiene has found that information about surface levels of contaminants may lead to better dermal exposure judgments or classifications. The NIOSH Manual of Analytical Methods (NMAM) includes chapters on specific areas of interest. Last year, the chapter “Surface Sampling Guidance, Considerations, and Methods in Occupational Hygiene” was added to NMAM. This chapter compiles available resources and provides additional guidance on surface sampling methods and strategies, drawing upon the history of surface sampling research at NIOSH, available consensus standards, and regulatory requirements for surface sampling and the research underpinning them. As one of the authors of the new chapter, I’ve compiled the following highlights from this new resource. SURFACE SAMPLING CHALLENGES Surface sampling campaigns can have many different objectives and target agents. For this reason, it’s unlikely that a single overarching resource can aid in the development of surface sampling plans for all scenarios. But some considerations apply to all surface sampling campaigns, and certain decisions need to be made and documented before samples are taken and the resulting data interpreted. The new NMAM chapter outlines these basic considerations and brings together the myriad resources available on sampling methods for individual agents or classes of agents. Given the imprecision of collection efficiency and the difficulty in carrying out campaigns that capture surface variability, the data obtained from surface sampling often involves more uncertainty than data from other common sampling methods, such as air sampling or biological monitoring. As with other kinds of sampling, the use of validated, standardized methods helps ensure the data is reliable and minimizes uncertainty to the extent possible. Understanding and controlling this uncertainty and maintaining consistency are key to ensuring data are interpreted and used appropriately. ESSENTIAL CONSIDERATIONS It is up to industrial hygienists to select the surface sampling method that meets performance requirements. Considerations for selection include the collection methods (for example, the medium, wetting agent, and sampling technique), locations for sampling, and the number of samples to collect. The new NMAM chapter describes available resources for making these decisions, which include standardized methods, consensus standards, and regulations and their accompanying guidance. The sample medium, wetting agent, and technique are selected based on the agent being sampled and the qualities of the surface, such as its texture, fragility, cleanliness, and loading (that is, the expected amount of deposited agent). It is important to understand the performance of the sampling method, such as its collection efficiency, for your specific target agent, surface type, and loading. Without this information, confidence in the resulting data may be low. A wetting agent can increase collection efficiency, but it has to be compatible with the target agent, the surface, and the analytical method; some wetting agents degrade the target agent, the surface, or both. A wide variety of media materials and formats are available, including vacuuming sample cassettes. Selection of medium—both materials and format—largely depends on the availability of standardized methods and data that can indicate how the medium influences performance. Together, sample medium, wetting agent, and collection technique will affect collection efficiency and the analytical or quantitative results. Many factors influence collection efficiency, including the physical or chemical bonds between the contaminant and the surface. Collection efficiency is typically determined via laboratory experiments prior to surface sampling, which are conducted to help the industrial hygienist understand whether the selected method meets expectations of performance. Consensus surface sampling methods have usually met known performance criteria, so attempting to identify an applicable consensus standard or validated method is an ideal first step.
The data obtained from surface sampling often involves more uncertainty than data from other common sampling methods.
Close communication with the selected analytical laboratory is essential to determine if the lab can perform the analysis as expected, if co-contaminants or sample media may interfere with analysis, or if surface loading will impact sensitivity or accuracy. Data quality depends on laboratory analysis methodologies and limitations. For example, sample compositing—combining multiple samples for one analysis—affects detection limits. The factors that contribute to data quality, uncertainty, and consistency are essential components of planning.
Once a method has been chosen, the other components of the sampling strategy—sample number and location—define how representative the data are and what inferences can be made from the data. Therefore, before sampling, these components should be chosen wisely and the decision-making process documented. Industrial hygienists have the option to conduct random sampling, targeted (judgment-based) sampling, or a hybrid of the two. Without some incorporation of random sampling, the bias in the data limits both its representativeness and the types of statistical comparisons that can be made. For this reason, targeted sampling is often used in emergent situations or in hybrid approaches and is followed by random sampling.
The new NMAM chapter points toward resources to help industrial hygienists understand how to develop a strategy that produces data to meet sampling goals. Products and research from EPA and the Pacific Northwest National Laboratory are available to assist in these decisions and to better understand how those choices impact representation and opportunities for statistical comparisons.
RESOURCES FOR INDUSTRIAL HYGIENISTS A core objective of the NMAM chapter on surface sampling was to bring useful resources together and put them into the hands of industrial hygienists. In the chapter, readers can find compilations of NIOSH surface sampling methods, standards on surfaces and dermal sampling from consensus organizations such as ASTM International and the International Organization for Standardization, and other resources on surface sampling methodology from OSHA and the Brookhaven National Laboratory.
The chapter compiles several types of surface sampling resources on methods and strategies. In developing the guidance, my coauthors and I made extensive use of available consensus standards. The organizations that develop consensus standards have published surface sampling methods for specific agents, like metals and biological agents. ASTM International has published several consensus standards for surface sampling for a wide variety of agents, including metals, asbestos, and fungi. The NMAM covers methods for surface and skin sampling, some of which are aligned with ASTM consensus standards.
The chapter touches upon surface contamination criteria or limits for certain substances. In the U.S., regulatory surface contamination limits have been established for lead, beryllium, and polychlorinated biphenyls, but they apply only in specific settings and are regulated by separate government agencies. Regarding occupational limits, OSHA requires surfaces to be “as free as practicable” of some metals and has provided some guidance for interpreting that phrase. ACGIH has published two TLV-SLs. But for most contaminants, criteria or limits have not been established.
The development of the chapter revealed gaps in information about surface sampling. Iterative assessment and revision of the chapter can incorporate additional research and resources to make them more widely available. As research progresses and additional questions arise, more information can be added to fill those gaps—about sampling methods, applications, strategies, and more.
ADDITIONAL RESOURCES AND TOOLS While the NIOSH chapter is a primer on surface sampling considerations, AIHA volunteer groups can offer dynamic support for industrial hygienists. AIHA has convened a Dermal and Surface Sampling Working Group, and the AIHA Exposure Assessment Strategies Committee has also supported the development of resources.
In summary, surfaces can say a lot about a workplace. However, careful consideration of the aims, methods, and strategies used in surface sampling campaigns is necessary for the resulting data to provide the information needed to make decisions about occupational health and safety interventions—and for understanding the limitations of the data. When considering surface sampling, the chapter “Surface Sampling Guidance, Considerations, and Methods in Occupational Hygiene” from the fifth edition of NMAM is a good place to start.
KENDRA BROADWATER, MPH, CIH, is a research industrial hygienist with NIOSH’s Western States Division. She has published over 25 articles and reports.
Disclaimer: The findings and conclusions in this report are those of the author and do not necessarily represent the official position of the National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention.
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Government Accountability Office: “Anthrax Detection: Agencies Need to Validate Sampling Activities in Order to Increase Confidence in Negative Results” (April 2005).
Journal of Occupational and Environmental Hygiene: “Accuracy of Professional Judgments for Dermal Exposure Assessment Using Deterministic Models” (March/April 2023).
NIOSH: “Surface Sampling Guidance, Considerations, and Methods in Occupational Hygiene,” in the NIOSH Manual of Analytical Methods, 5th ed. (PDF, August 2022).
The Synergist: “What’s on Your Workplace Surfaces? Surface Sampling, Consensus Standards, and Laboratory Analysis” (August 2020).