Wednesday 16 May 2012

Occupational Skin Exposure

  1. INTRODUCTION

    The purpose of this chapter is to provide guidance to OSHA Compliance Safety and Health Officers (CSHOs) and to the industrial hygiene community on the potential for skin exposure to chemicals in the workplace and the available means of assessing the extent of skin exposure. Skin exposure to chemicals in the workplace is a significant problem in the United States (U.S.). Both the number of cases and the rate of skin diseases in the U.S. exceed recordable respiratory illnesses. In 2006, 41,400 recordable skin diseases were reported by the Bureau of Labor Statistics (BLS) at a rate of 4.5 injuries per 10,000 employees, compared to 17,700 respiratory illnesses with a rate of 1.9 illnesses per 10,000 employees.1

    In addition to causing skin diseases, many chemicals that are readily absorbed through the skin can cause other health effects and contribute to the dose absorbed by inhalation of the chemical from the air. Skin absorption can occur without being noticed by the employee and in some instances may be a more significant route of exposure than the respiratory system. This is particularly true for non-volatile chemicals that are hazardous and which remain on work surfaces for long periods of time. The number of occupational illnesses caused by skin absorption of chemicals is not known. It is, however, argued that of an estimated 60,000 deaths and 860,000 occupational illnesses per year in the U.S. attributed to occupational exposure, even a relatively small percentage caused by skin exposure would represent a significant health risk.2


  2. BASICS OF SKIN EXPOSURE

    Skin contact with chemicals can result in irritation, allergic response, chemical burns, and allergic contact dermatitis. Irritant dermatitis may be caused by a variety of substances such as strong acids and bases. Some examples of chemicals which are potent irritants include: ammonia, hydrogen chloride, and sodium hydroxide. Generally, primary irritants produce redness of the skin shortly after exposure with the extent of damage to the tissue being related to the relative irritant properties of the chemical. In most instances, the symptoms of primary irritation are observed shortly after exposure; however, some chemicals produce a delayed irritant effect because the chemicals are absorbed through the skin and then undergo decomposition with aqueous portions of the skin to produce primary irritants. Ethylene oxide, epichlorohydrin, hydroxylamines, and the chemical mustard agent (bis(2-chloroethylsulfide)) are classic examples of chemicals which must first decompose in the aqueous layers of the skin to produce irritation.

    Allergic contact dermatitis, unlike primary irritation, is caused by chemicals which sensitize the skin. This condition is usually caused by repeated exposure of the skin to a relatively low concentration chemical which ultimately results in an irritant response. Frequently, the sensitized area of skin is well defined, providing an indication of the area of the skin which has been in contact with the sensitizing material.

    A wide variety of both organic and inorganic chemicals can produce contact dermatitis. Some examples of these chemicals include: aromatic nitro compounds (e.g., 2,4-dinitrochlorobenzene), diphenols (e.g., hydroquinone, resorcinol), hydrazines and phenylhydrazines, piperazines, acrylates, aldehydes, aliphatic and aromatic amines, epoxy resins, many other organic chemicals, and metals (e.g., hexavalent chromium). These substances can also produce contact sensitization. Allergic contact dermatitis is present in virtually every industry, including agriculture, chemical manufacturing, rubber industry, wood, painting, bakeries, pulp and paper mills, and many others.

    Lastly, there is a class of chemicals which can produce allergic reactions on the skin after exposure to sunlight or ultraviolet (UV) light. These chemicals are called photosensitizers. Polynuclear aromatic compounds from coke ovens and the petroleum-based tars are examples of chemicals which can be photoactivated on the skin to cause an irritant response.


    3. A. Skin Absorption

    In addition to the effects that chemicals can directly have on the skin, the skin also acts as a pathway for chemicals to be absorbed into the body. The skin primarily consists of two layers - the epidermis and the dermis. The outer layer of the epidermis is composed of a compacted layer of dead epidermal cells called the stratum corneum which is approximately 10 − 40 micrometers thick. The stratum corneum is the primary barrier for protection against chemical penetration into the body. Its chemical composition is approximately 40% protein, 40% water, and 20% lipid or fat. Because skin cells are constantly being produced by the body, the stratum corneum is replaced by the body approximately every two weeks.

    Chemical absorption through the stratum corneum occurs by a passive process in which the chemical diffuses through this dead skin barrier. Estimates of the amount of chemicals absorbed through the skin as discussed below assume that the chemicals passively diffuse through this dead skin barrier and are then carried into the body by the blood flow supplied to the dermis.

    A number of conditions can affect the rate at which chemicals penetrate the skin. Physically damaged skin or skin damaged from chemical irritation or sensitization will generally absorb chemicals at a much greater rate than intact skin. Organic solvents which defat the skin and damage the stratum corneum may also result in an enhanced rate of chemical absorption. If a chemical breakthrough occurs while wearing gloves or other protective clothing, the substance becomes trapped against the skin, leading to a much higher rate of permeability than with uncovered skin. An employee who wears a glove for an extended period of time experiences enhanced hydration to the skin simply because of the normal moisture which becomes trapped underneath the glove. Under these conditions, chemical breakthrough or a pinhole leak in a glove can result in greater chemical absorption due to increased friction, contact time with the substance and increased temperature resulting in a higher overall absorption through the skin. In another example, an employee may remove a glove to perform a task which requires increased dexterity, exposing the skin to additional chemical exposure even after redonning the glove.

  3. RISK ASSESSMENT (ESTABLISHING A SIGNIFICANT RISK OF SKIN EXPOSURE)

    The absorption of chemicals through the skin can have a systemic toxic effect on the body. In many instances dermal exposure is the principal route of exposure, especially for chemicals which are relatively non-volatile. For example, biological monitoring results of coke oven workers coupled with air monitoring of the employees’ exposure demonstrated that 51% of the average total dose of benzo[a]pyrene absorbed by coke oven workers occurred via skin contact.3 Studies of employees in the rubber industry suggest that exposure to genotoxic chemicals present in the workplace is greater via the skin than via the lung.4

    For chemicals which are absorbed through the skin and which are hazardous, the levels of exposure on the skin must be maintained below a level at which no adverse effects would be observed. One of the simplest ways of determining this amount is to estimate the amount of a chemical which can be absorbed into the body based upon an air exposure limit. For example, the OSHA permissible exposure limit (PEL) for methylenedianiline (MDA) is 0.1 part per million (ppm), or 0.81 milligrams per cubic meter (mg/m3). If we assume that the average employee breathes 10 m3 of air a day, and further assume that all of the MDA is absorbed from the air at the PEL, then the maximum allowable dose to the body per day becomes:

    (0.81 mg/m3)(10 m3) = 8.1 mg maximum allowable dose to the body for MDA

    In addition to using OSHA PELs, American Conference of Governmental Industrial Hygienist (ACGIH) Threshold Limit Values (TLVs) or internal corporate air concentration values can also be used to establish the maximum allowable dose in the same manner. This method assumes that the toxic effects of the chemical are systemic and that the toxicity of the chemical is independent of the route of exposure.

    The lethal dose to the skin which results in death to 50% of exposed animals (LD50 dermal) is also a useful comparative means of assessing dermal exposure hazards. The OSHA definition of a toxic chemical (defined in 29 CFR 1910.1200 App. A) as it relates to skin exposure is a chemical which has a "median lethal dose (LD50) of more than 200 milligrams per kilogram but not more than 1000 milligrams per kilogram of body weight when administered by continuous contact for 24 hours (or less if death occurs within 24 hours) with the bare skin of albino rabbits weighing between two and three kilograms each." If available, the no observable effect level (NOEL) can also be useful in establishing a safe exposure level. Skin notations or skin designations for chemicals listed as ACGIH TLVs or the OSHA PELs are also useful guides; however, many chemicals (e.g., hexone, xylene and perchloroethylene) which can pose a dermal hazard are not designated.

    A. Estimating the Extent of Absorption of Chemicals through Skin

    For exposure to chemicals which are recognized as systemic toxins, that is, chemicals which are toxic once absorbed into the bloodstream, the route of exposure to the chemical is not important. Hence, the maximum allowable dose can be used as a basis for determining if a chemical poses a skin exposure hazard.

    The extent of absorption of a chemical through the skin is a function of the area of the exposed skin, the amount of the chemical, the concentration of the chemical on the skin, the rate of absorption (flux rate) into the skin, and the length of time exposed.5 Assume for example, that an employee has contact on the interior portion of both hands to a solution of phenol (10% solution by weight) for two hours. Approximately how much phenol would be absorbed? The flux rate, J, is determined by:

          J = (Kp)(Concentration of Chemical on Skin)

          Kp for phenol = 0.0043 cm/h (Kp values available from Exhibit B-2 in EPA Dermal guide6)
          (Kp – skin permeability coefficient)

    Thus, at a concentration of 10% by weight (10 g/100 cm3, 10,000 mg/100 cm3, or 100 mg/cm3)

          J = (0.0043 cm/h)(100 mg/cm3) = 0.43 mg/(cm2•h)(flux rate)

    Hence, under these conditions, 0.43 mg of phenol will be absorbed through the skin per cm2 of exposed skin per hour.

    Therefore, the absorbed dose of phenol through the skin of an employee's two hands (both palms exposed – approximate area: 840 cm2) would be determined by:

    Absorbed Dose = (840 cm2)(0.43 mg/( cm2•h)) (2 h) = 722 mg absorbed over a 2-hour period. This compares to an allowable dose (PEL = 19 mg/m3) via the lung for an 8-hour exposure of (19 mg/m3)(10 m3) = 190 mg. Hence, this 2-hour exposure via the skin would represent absorption of phenol which is 3.8 times the allowable dose via the lung.

    The following hypothetical example illustrates the relative importance of skin absorption as a factor in exposure. Let us assume that an employee is wearing gloves and the gloves are exposed to a phenol solution. Let us further assume that the penetration through the gloves is detected by a hand wipe sample, and that 75 mg of phenol is reported present from a water hand rinse of the employee’s hands taken before lunch. Let us further assume that the amount of phenol detected inside the glove at the lunch break represents a uniform constant exposure which occurred shortly after the beginning of the work shift. Finally, let us further assume that the 75 mg of phenol is present in approximately 10 milliliter (mL) of water (perspiration) present on the surface of the skin. How much phenol was absorbed in the 8-hour period?

    First, we determine the flux rate: J = (0.0043 cm/h)(75 mg/10 cm3) = 0.0322 mg/(cm2•h) (flux rate)

          Absorbed Dose = (840 cm2)(0.0322 mg)/(cm2•h)(8 h) = 216 mg of phenol absorbed

    Hence, the estimated amount of phenol absorbed into the body is greater than the maximum allowable amount of phenol based upon inhalation of 190 mg.

    B. Glove Permeability

    Penetration of chemicals through gloves is similar to the penetration of chemicals through the skin. Glove manufacturers publish breakthrough data which reflect the length of time which occurs before a chemical penetrates through a particular type of glove material. These tests are performed using ASTM (American Society for Testing and Materials) Method F 739 in which a pure, or neat, chemical is placed on one side of a section of the glove material and the time to penetrate through the glove is measured by analyzing the air on the other side of the glove to detect chemical breakthrough.

    Unfortunately, these breakthrough times can be misleading because actual breakthrough times will typically be less than reported by the manufacturer. This is the case because the temperature of skin is greater than the test temperature, and this results in an increased permeability rate. Secondly, glove thinning occurs along pressure points where an employee may grip a tool or otherwise exert pressure on an object while wearing a glove. Glove degradation and reuse of gloves can also dramatically reduce the effectiveness of a glove’s chemical permeability. Additionally, only limited breakthrough data for solvent mixtures is available and in many cases the breakthrough time for a solvent mixture is considerably less than would be predicted from the individual breakthrough times for each of the individual solvent components. Finally, batch variability can also result in wide variations in breakthrough times from one glove to the next.7 These differences, and possibly greater differences, would be expected to occur when comparing a similar glove type produced by different manufacturers.

    As a result of these limitations, it is necessary that the employer evaluate glove selection and use to prevent employee exposure as specified in 29 CFR 1910.132(d). Guidance on conducting in-use testing methods for glove selection is available.8

    Direct Reading Patches/Charcoal Felt Pads

    In some instances, direct reading patches and/or bandage-type patches can be worn inside a glove to demonstrate directly through a color change that an exposure has occurred. In other instances, charcoal felt patches or bandages can be worn which can be analyzed by a laboratory to establish the presence of glove penetration by volatile organic chemicals. These charcoal pads may also be used for detection of less volatile organic chemicals. However, poor sample recoveries from a charcoal surface for higher molecular weight substances may result in underestimating the extent of skin exposure for these types of chemicals.

    When sampling inside a glove, OSHA recommends that employees being sampled wear disposable gloves inside their normal PPE, with the indicator/charcoal felt pads being placed on the disposable glove surface. Placing the pad on the disposable glove between the skin surface and the regular PPE eliminates any potential skin exposure from the chemicals used in the colorimetric pads, and also reduces any effects that perspiration might have on the sampling pads.

    For inside–the–glove sampling, it also is advisable to use a control pad to measure the concentration of airborne volatile chemicals. This control pad should be attached to the employee’s clothing while the employee performs his/her normal tasks. The glove sample result would then be corrected for the amount of the organic chemical in the airborne sample to determine the amount of organic chemical actually permeating the protective glove relative to the amount of organic chemical entering the glove opening. This procedure, therefore, would allow the sampler to identify the possible route of glove contamination.


  4. BIOLOGICAL MONITORING

    Biological monitoring is defined by the American Industrial Hygiene Committee on Biological Monitoring as "the assessment of human exposure through the measurement of internal chemical markers of exposure, such as the chemical agent itself and/or one of its metabolites or an exposure related biochemical change unrelated or related to disease, in human biological samples."9 Biological monitoring can be a useful technique for determining if dermal exposure is a significant contributor to the employee's overall exposure. For example, in a work environment in which the air exposure to a specific chemical is well controlled, or well characterized, an abnormally elevated biological monitoring result will likely indicate that skin or ingestion is a major mode of exposure. Coupled with evidence of surface contamination, and documentation of poor or non-existent personal protection against chemical skin exposure, biological monitoring can be a valuable means of documenting dermal exposure to a chemical.

    Presently, there are a limited number of guidance values for chemicals measured in the body. The major sources of these values are published by the ACGIH and are known as biological exposure indices or BEIs. In addition to the 45 chemicals for which a BEI has been established, the American Industrial Hygiene Association (AIHA) has developed a BEEL, or biological environmental exposure level, to more directly develop guidance values for chemicals which have the skin as their primary mode of exposure. Currently, one chemical, methylenedianiline (MDA), has an established BEEL.

    Finally, there are many studies in peer reviewed literature that report exposure levels for numerous chemicals measured as biological matrices; these studies address exposures for employees in a variety of occupations and industries. These studies can be useful, in a comparative fashion, for assessing the extent of exposure between exposed and unexposed employees when the workplace in the study involves the same conditions (e.g., chemical exposure, type of work) as the workplace being inspected.

    A. Guidance on Biological Monitoring Methodology

    In the event that a CSHO believes biological monitoring would be valuable to assess and evaluate employee exposure to a substance or mixture of substances, they should first contact their Regional office, the Salt Lake Technical Center and the Office of Occupational Medicine to determine the most effective approach and technique to obtain the desired result. Biological sampling requires special consideration and will be addressed on a case–by–case basis.

    Biological monitoring results can be used to demonstrate significant skin absorption, ingestion or airborne exposures. For instance, when wipe/skin sampling has confirmed exposure, a voluntarily obtained employee biological sample may prove useful in documenting that skin exposure to the chemical of concern has occurred. Ideally, it is desirable to have samples from a number of employees who are suspected of being exposed. Also, control samples from individuals who do not have skin exposure, or are suspected of much less exposure, are valuable.

    For biological sampling, proper sampling containers and a protocol for handling and shipping samples need to be addressed. In general, a qualified laboratory which is experienced in the analysis of biological samples will provide sample vials, shipping containers, and the technical expertise to properly collect, store and ship specimens.

    B. Review of Employer Biological Monitoring Results

    In instances in which an employer has been conducting biological moni¬toring, the CSHO shall evaluate the results of such testing. The results may assist in determining whether a significant quantity of the toxic ma¬terial is being ingested or absorbed through the skin. However, the total body burden is composed of all modes of exposure (e.g., inhalation, ingestion, absorption and injection). For the CSHO to assess the results of the biological monitoring, all the data (including any air monitoring results) must be evaluated to determine the source(s) of the exposure and the most likely mode(s) of entry.

    Results of biological monitoring which have been voluntarily conducted by an employer should not be used as a basis for citations. In fact, OSHA promotes the use of biological monitoring by employers as a useful means for minimizing exposures and for evaluating the effectiveness of control measures.

    Citations, in consultation with the Regional Office, would be appropriate when biological monitoring results indicate an unacceptable level of exposure, and the employer is unable to demonstrate that meaningful efforts to reduce or control the exposure(s) were taken.


  5. WIPE SAMPLING METHODOLOGY

    A. Surface Wipe Sampling

    Wipe sampling to establish the presence of significant surface contamination is useful for documenting hazards. A reference control wipe sample or samples taken from areas in which exposure is not anticipated will also help to establish the relative amount of surface contamination.

    In instances where surface contamination is suspected and the employer has not required the use of effective Personal Protective Equipment (PPE) for employees in these areas, wipe sampling may be an effective means of documenting that a skin hazard exists.

    In many instances, several wipe samples taken in an area suspected of being contaminated may be useful. For example, some surfaces which would be expected to be contaminated with chemicals because of airborne deposition of a non-volatile chemical may actually be relatively free of surface contamination because of frequent contact of the surface by the employee (i.e., frequently contacted surfaces may be expected to be "clean" because of frequent employee contact). Wipe samples of frequently contacted surfaces in conjunction with less frequently contacted surfaces in the same vicinity can be useful to establish the likelihood that skin exposure is occurring in "clean" areas in which PPE is not being used, or is being improperly used. Wipe sampling can help establish that a significant amount of surface contamination is present in areas in which employees are not effectively protected by PPE.

    Housekeeping may also be demonstrated by wipe samples which show major differences in surface contamination between work areas that have been routinely cleaned and areas which have not been recently cleaned. This sampling would allow the CSHO to demonstrate the employer’s failure to maintain a clean work area.

    Wipe samples taken inside the sealing surface of "cleaned" respirators can also establish the absence of an effective respiratory protection program.

    Templates which are used to define a relatively constant surface area for obtaining a wipe sample are generally not necessary. Templates also cannot be used except on flat surfaces, and they can cause cross-contamination if the template is not thoroughly cleaned between each use. Additionally, the CSHO may want to sample a much larger surface area than the area covered by the template. This is particularly true if the CSHO wants to determine the cleanliness of a lunch table or other large surface area. In all cases, the CSHO should measure the dimensions of the area being sampled and record this value on Form OSHA-91A because the mass amount of chemical measured by the laboratory will be used to determine the mass per area for the wipe sample.

    B. Skin Sampling

    Skin wipe samples taken on potentially exposed areas of an employee’s body are a useful technique for demonstrating exposure to a recognized hazard. For water-soluble chemicals, a wipe pad moistened with deionized water can be used to wipe the skin. Generally, the best procedure is to allow employees to use the wipe pad to clean their skin surfaces, and then have them insert the wipe pad into a clean container, which is labeled and sealed. Hands, forearms, faces, and possibly feet may be exposed to contaminants that a wipe sample of the skin can be used to establish exposure. Include a blank water sample and use only deionized water, or another source of water approved by the laboratory, for analysis purposes.


  6. ENFORCEMENT RECOMMENDATIONS

    There are currently no surface contamination criteria or quantifications for skin absorption included in OSHA standards. However, some OSHA standards contain housekeeping provisions that address the issue of surface contamination. Exposures to various chemicals (e.g., formaldehyde, methylenedianiline, and methylene chloride) are addressed in specific standards for general industry, construction, and shipyard employment. Useful information on dermal exposure standards can be found at Dermal Exposure - OSHA Standards Safety and Health Topics Page.

    Despite the lack of specific criteria or quantitative data for use in the enforcement of elevated exposures to surface and skin chemical hazards in the workplace, it is well established that skin exposure and ingestion of chemicals is a significant mode of occupational exposure. In instances in which a hazard can be established which is not addressed in a specific OSHA standard, the compliance officer may consider a 5(a)(1) General Duty Clause citation to address this concern.

    In lieu of issuing a 5(a)(1) citation, it is suggested that alternative citations can be issued either under OSHA standards addressing sanitation (29 CFR 1910.141), hazard communication (29 CFR 1910.1200), personal protective equipment (29 CFR 1910, subpart L), exposure to hazardous chemicals in laboratories (29 CFR 1910.1450), or pertinent standards dealing with construction (29 CFR 1926) and shipyard employment (29 CFR 1915). In instances where a high degree of surface contamination is evident, or clear evidence exists to establish skin exposure of employees to a recognized hazard, then 29 CFR 1910.141(a)(3) can be cited. That is, the CSHO can readily establish that the employer has failed to keep the workplace "clean to the extent that the nature of the work allows." Alternatively, 29 CFR 1910.1200(h) can be cited based upon the evidence collected by the CSHO to demonstrate that the employer failed to adequately inform and train employees on the hazards present in the workplace.

    Finally, a specific citation may be issued for deficiencies in PPE use designed to protect employees from skin exposure under 29 CFR 1910.132, which requires that the employer evaluate the hazards, select proper PPE, and train employees on proper use of the PPE.


  7. REFERENCES

    1. Bureau of Labor Statistics. "Nonfatal occupational illnesses by major industry sector and category of illness, private industry, 2006" U.S. Department of Labor (DOL), 2007 (20 February 2008).


    2. Boeniger, M.F. Invited Editorial. "The Significance of Skin Exposure." Ann. Occup. Hyg. 47(2003): 591-593.


    3. VanRooij, J.G.M. et al. "Estimation of Individual Dermal and Respiratory Uptake of Polycyclic Aromatic Hydrocarbons in 12 Coke Oven Workers." Br. J. Ind. Med. 50(1993): 623–632.


    4. Vermeulen, R.; Bos, R.P.; Kromhout, H. "Exposure Related Mutagens in Urine of Rubber Workers Associated with Inhalable Particulate and Dermal Exposure." Occup. Environ. Med. 60(2003): 97-103.


    5. Kanerva, L.et al. Handbook of Occupational Dermatology. Berlin Heidelberg: Springer – Verlag, 2000.


    6. Risk Assessment Guidance for Superfund Volume I: Human Health Evaluation Manual (Part E, Supplemental Guidance for Dermal Risk Assessment), Jul 2004, EPA/540/R/99/005; OSWER 9285.7-02EP; PB99-963312. (11 December 2007).


    7. Klingner, T.D. and Boeniger, M.F. "A Critique of Assumptions About Selecting Chemical-Resistant Gloves: A Case for Workplace Evaluation of Glove Efficacy." Appl. Occup. Environ. Hyg. 17(2002): 360-367.


    8. Klingner, T.D. and Boeniger, M.F. "In-Use Testing and Interpretation of Chemical-Resistant Glove Performance." Appl. Occup. Environ. Hyg. 17(2002): 368-378.


    9. Biological Monitoring – A Practical Field Manual. Shane Que Hee, Ed.; AIHA Publication: AIHA, 2004.

APPENDIX II: 2–1. GENERAL PROCEDURE FOR COLLECTING WIPE SAMPLES
Preloading a group of vials with sampling filters (consult the OSHA Chemical Sampling Information files to determine appropriate sampling media to use) is a convenient method to carry the sample media to the worksite. (Smear tabs should be inserted with the tab end out.) Clean disposable gloves should be worn when handling the filters and smear tabs. The gloves should not be powdered.

The following are general recommendations for taking wipe samples. Consult the Chemical Sampling Information files for more specific instructions.
  1. Record each location where a wipe sample was taken. Photographs, sketches, and other means of noting sampling locations are helpful.


  2. A new set of clean, disposable gloves should be used for each sample to avoid contamination of the filter by previous samples (and the possibility of false positives) and to prevent contact with the substance.


  3. Withdraw the filter from the vial with your fingers or clean tweezers. If a damp wipe sample is desired, moisten the filter with distilled water or other solvent as recommended. NOTE: For skin sampling use only water. Other solvents may be appropriate for wiping surfaces depending upon the type of chemical being
    4. sampled.

  4. Depending on the purpose of the sample, it may be useful to determine the concentration of contamination (e.g., in micrograms of agent per area). For these samples, it is necessary to record the area of the surface wiped (e.g., 100 cm2). This would normally not be necessary for samples taken to simply show the presence of the contaminant.


  5. Firm pressure should be applied when wiping.


  6. Using the filter, wipe an area about 100 cm2, rubbing the entire area side to side, then up and down. In many cases (such as knobs and levers) it may not be possible to wipe 100 cm2.


  7. Place the filter in a sample vial, cap and number it, and note the number at the sample location. Include notes which will provide any additional relevant details regarding the nature of the sample (e.g., "Fred Employee's respirator, inside"; "Lunch table").


  8. At least one blank filter treated in the same fashion, but without wiping, should be submitted for each sampled area.


  9. Some substances (e.g., benzidine, hexavalent chromium, 4,4'-methylenedianiline) are unstable and may require a solution to be added to the vial as soon as the wipe sample is placed in the vial or may require other special sample handling. If such instability is suspected, check the OSHA Chemical Sampling Information file for sample handling instructions or contact SLTC for guidance.


  10. Submit the samples, each sealed with a Form OSHA-21, and in accordance with procedures located in OTM Chapter 4, to the SLTC with a completed Form OSHA-91A.
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