SELECTING CHEMICAL-PROTECTIVE CLOTHING
Part 2: Permeation Test
FIREFIGHTERS and others involved in hazardous-materials incidents often have little information at their disposal for selecting chemicalprotective clothing. While most haz-mat teams make their best effort to choose clothing that offers adequate protection, in many cases a large degree of uncertainty exists. Lack of documented clothing chemical resistance data or its misuse may lead to wearing clothing that is potentially unsafe for many of the situations responders encounter. Moreover, many situations are uncharacterized and involve unidentified chemicals or mixtures of several chemicals that may be reacting synergistically. In the absence of reliable clothing recommendations, actual on-site testing may be the only way of ensuring appropriate clothing selection. The use of a permeation field test can help solve these selection problems.
SUIT SELECTION PROBLEMS
Haz-mat response teams make two selection decisions with respect to chemical-protective clothing—what to buy and when to use it. The first decision involves selecting a protective suit that will hopefully protect wearers for the majority of incidents to which they respond. Usually, the haz-mat team must acquire an inventory of different suits, garments, gloves, and boots to cover a range of incidents. The second decision is much more difficult and tests the first decision, that being the selection of a specific protective suit and related protective clothing for a given incident.
The difficulty in making on-site protective clothing decisions lies in having the right kind of information available to the team leader so he can choose adequate protection for his team members. The first part of this process involves identifying the hazards present by characterizing the situation, identifying the chemicals involved, defining the hazards of those chemicals, and anticipating other factors (e g., temperature, type of physical environment) that will affect a response effort. The second step involves cross-referencing the gathered incident data with known values or recommendations from one or more of the following sources:
- Comprehensive clothing selection guides
— DOT Emergency Response Handbook
— Guidelines for Selecting Chemical Protective Clothing
— CAMEO computer database
— GlovES + portable disk database;
- Vendor (clothing manufacturer) literature;
- Standard operating procedures. Ideally, the team leader can then determine which suit, glove, and boot will allow team members to operate safely within the hot zone.
Unfortunately, most haz-mat incidents are not ideal. In consulting available sources, the team leader may find that the suit he has is not listed or not recommended for that particular chemical; he may be confronted with an unidentified chemical with unknown hazards or a mixture of chemicals for which there are no recommendations; he may have to use “generic” data (not based on his specific suit) and wonder if the material in the garment he selects is really similar to the “generic” materials; he may find a suit material that appears to be good but doesn’t know or can’t find out if the suit visor or gloves will provide the same level of protection. These are only some of the situations that present themselves when team leaders make the critical decision of selecting the right chemical-protective suit and accessories.
MAKING GOOD CHOICES
The only way to increase your confidence in making an appropriate clothing selection is to have the proper information available for the specific chemicals involved. In situations where no contact with the chemical or its vapors is permissible, the proper information is permeation data —breakthrough times and permeation rates. The general practice for using this data is to find a material that has a breakthrough time greater than the anticipated period of exposure. Relatively low permeation rates are also desirable when breakthrough times are marginal. The permeation data on which recommendations are based should meet the following criteria:
- Testing should be done in accordance with ASTM Standard F739. This standard defines the procedures for conducting permeation tests and allows end users to compare data from one product to another consistently. Recommendations that are based on appropriate testing methods should cite this standard.
- Test results should he specific to the suit or clothing item under consideration. Data or recommendations given for generic classes of materials such as butyl rubber, neoprene, and PVC may not be representative of the product you are using. In other words, a nitrile rubber glove from manufacturer “A” may protect against a specific chemical, whereas a nitrile glove from manufacturer “B” may not provide protection against the same chemical. Substantial differences in the chemical resistance of generic materials have been measured and documented in previous laboratory tests.
- Test data should be provided for all major materials comprising the garment or protective ensemble being worn. Using recommendations based on the suit material only is not sufficient to determine the protection the complete garment offers. The garment is only as good as its weakest component: The visor, gloves, and boots also need to be tested, with the poorest performing component being the limiting material for basing overall garment use recommendations.
Most comprehensive selection guides do not provide information that meets all the criteria above. Oversimplified guides such as the DOT Emergency Response Guidebook cannot make the most accurate protective clothing recommendations. The guidebook does not recommend specific clothing and in some cases states that structural firefighting clothing is sufficient against some chemicals.
Other references such as Guidelines for the Selection of Chemical Protective Clothing make specific material recommendations for a large number of chemicals and distinguish whether the recommendations are based on quantitative test data or qualitative observations. However, recommendations are made for generic classes of material such as natural rubber, neoprene, and butyl and not for specific clothing items. Again, the danger in this practice is having a material that does not perform as well as its generic counterpart. Though Guidelines does provide a volume containing the data used for making the recommendations, it is difficult to interpret this information. For the most part, Guidelines serves well for an initial survey of clothing chemical resistance but does not provide the complete picture.
GlovES+ is a computerized chemical-protective clothing database and expert system similar to Guidelines but it lets users decide the criteria for clothing selection. It has the advantage of showing users the exact data available for specific products. However, none of the results going into the database are screened and therefore may be inaccurate or not obtained through standard test methods. Also, most of the data is for gloves; very few results cover protective suits or other full body garments.
The CAMEO system, which includes a module for protective clothing selection, is another computerized database. In its current version, it incorporates a computerized version of Guidelines without the test data.
The best source of data comes from the manufacturer and is included with the product. It is usually up-to-date and specific to the product. It is important, however, that team leaders or others who select protective clothing review this data cautiously. These clothing recommendations must also be based on quantitative permeation data and cite the ASTM F739 method. If simple recommendations are made with no supporting data, you cannot be sure that the recommendations are based on appropriate testing. Many manufacturers are now reporting permeation data for their products. Unfortunately they provide data on a limited number of chemicals and only for the garment material — not the visor, gloves, or boots. Despite the wealth of data on protective clothing chemical resistance, haz-mat teams still encounter many situations where the right kind of information is not available.
PERMEATION FIELD TEST
The ability to easily test representative samples of protective clothing material against chemicals as they occur in the field may be the only viable approach for getting the information that team leaders need to select adequate protective garments. Other groups faced with similar problems (such as hazardous-waste site cleanup) have endeavored to develop field methods that allow a simple and quick assessment of protective clothing chemical resistance. Both the National Institute for Occupational Safety and Health (NIOSH) and the Environmental Protection Agency (EPA) have investigated different methodologies for field test kits. The most successful effort was undertaken by Arthur D. Little, Inc. for the EPA. It found a method based on weight change to be the best indicator of material performance as compared to laboratory definitions. This technique is commonly referred to as the “permeation cup” method. Prototype test kits based on this method were found to best meet the following criteria set by the EPA:
- The test provides an estimate of breakthrough time and permeation rate.
- The kit should be durable, portable, self-contained, and require no external powder. (The requirement for no external power was later dropped when the EPA found that AC power was generally available at the sites where the kit would be used.)
- The method should be easy to learn with minimum steps and training.
- The method should accommodate a wide range of chemicals or chemical mixtures.
The method involves filling a shallow, cup-shaped vessel with the liquid to be tested, clamping a material over the chemical, inverting the cell, and making periodic weighings of the assembly for a specified period of time. If the chemical permeates the material specimen, the assembly loses weight. When the weight change is detectable within the accuracy of the balance, a permeation breakthrough time is noted. By recording and plotting weight change, you can determine the permeation rate.
The method is currently being considered by the American Society for Testing and Materials F23 as a standard. The introduction of such a standard requires that several laboratories conduct the test in the same material-chemical parts and compare results to demonstrate the method’s accuracy. The permeation cup test has been subjected to both an interlaboratory round-robin testing and some field testing. In a round-robin test, nearly all laboratories found similar results.
Field tests by hazardous-waste site cleanup companies and firefighter hazmat teams demonstrated the ease and values of the portable kit in field settings. The field data collected compared well with many of the laboratory permeation test results.
HOW IT WORKS
The permeation cup method is based on measuring weight loss. The method requires the following components: field-rugged, portable analytical balance (accurate to ± 0.01 g); permeation cups; permeation cup stands; a template kit with stencil, scissors, and marker; a Teflon beaker; a graduated cylinder (10 ml); a calibrated weight (100g); data forms; and a carrying case.
The test consists of the following steps:
- Cut material specimens from representative protective garment switches using stencil, scissors, and marker. Weigh each material specimen individually. (All purchasers of haz-mat protective clothing should secure a quantity of test swatches from the manufacturer.)
- Connect the balance to a 110-volt AC source, level, check for zero, and calibrate with the 100-gram weight.
SOME APPLICATIONS OF A PERMEATION TEST
- Industrial sector. The permeation test can be a valuable criterion on which to base purchase selection of haz-mat protective clothing for industrial fire brigades. The test will indicate which brands of clothing are best suited for handling the chemical(s) manufactured, stored, and/or transported by the chemical company.
- Initial haz-mat response. The permeation method tests the compatibility of protective clothing on hand at the incident site with samples of an unknown material. The incident commander or team leader can then make a choice as to what clothing will best work for the situation at hand.
- Ongoing or completed haz-mat incidents. The permeation test can be ongoing during the incident and monitored for behavior of the known chemical spill on the protective clothing assemblies in use. A variation in the listed permeation data will encourage additional medical protocols.
- Measure and record the initial weight of material specimen.
- Collect a chemical sample with a beaker. Pour 10 milliliters of the liquid into each of three permeation cups using the beakers. For unidentified chemicals, trained personnel outfitted in the highest level of protective clothing available must collect the sample.
- Place the material specimens on the top of the cup and screw the top flange into place, clamping the material over the chemical.
- As soon as the permeation cup with chemical and material is assembled, invert and weigh the cup at time zero. Following the weighing, remove the cup from the balance and place on its holder in an inverted position, causing the chemical to be in direct contact with the material. The stand allows air to flow underneath the material to remove permeating vapor.
- Conduct additional weighings. The recommended periods of these weight measurements are at 3, 6, 9, 12, 15, 20, 25, 30,40, 50, and 60 minutes following assembly of the cell. You can use any weighing schedule as long as it covers the anticipated period of wearer exposure.
At any time that the weight loss exceeds .05 grams, the material is considered to have failed the compatibility test for that chemical.
- The test operator records the weight of the cup assembly at each weighing and calculates weight change and permeation rate (if applicable). Where three successful weight losses occur, the first time at which the loss is observed is the breakthrough time for the material-chemical pair tested. If the permeation rate is approximately constant during the last weight measurements (within 10 to 20 percent), it is said to be the steady-state permeation rate. If the rate continues to increase without any leveling off, it is called a maximum observed permeation rate.
- Remove the material specimen from the cup assembly, blot dry with paper towels or similar absorbent tissue, and weigh separately. The weight of the sample before and after exposure helps to determine material weight gain or loss. This measurement can serve as an indication of extensive material swelling or degradation.
Though the test is recommended to run an hour, it can be run for any period of time. However, running it for less than 15 minutes will not guarantee accurate results. Besides breakthrough time and permeation rate, the test operator can observe any significant changes in the appearance of the specimen during the test or following its removal, including material weight gain or deterioration. These observations may or may not be linked to the noted permeation behavior. Some samples may discolor or swell without measured permeation. In most cases, however, materials will show no visible changes when permeation does occur In any case, noting specimen appearance is another piece of information for evaluating material performance against the test chemical(s).
Table 1
Sample Results from Permeation Field Test Kit
Material: Neoprene (glove material)
Chemical: Acetone
Initial Specimen Weight: 3.96 gm
Final Specimen Weight: 4.40 gm
Percent Specimen Weight Change: 15.7%
Observations: Moderate swelling of specimen
* Total Weight Loss = Cup Weight (1st time interval) – Cup Weight (2nd time interval) Permeation Rate = Total Weight Loss/(exposed specimen area X time interval of change)
The chart at left shows sample results of using the field test kit method with acetone and a neoprene glove material. In this case, the operator was able to determine that acetone has a breakthrough time of 12 minutes after contacting the material and was able to calculate an approximate steady state permeation rate. A maximum permeation rate of 0.30 mg/cm2/min was calculated. In this test the results indicate that neoprene is incompatible with acetone.
APPLICATIONS AND BENEFITS
A permeation field test provides three pieces of information: breakthrough time, permeation rate, and visual observations for the specific material and chemical(s) tested. A kit can therefore be deployed in the field during haz-mat operations and used when uncertainty exists in the relative protection offered by a protective clothing ensemble. Results provided by the method increase the information available to the team leader or other authority making protective clothing selection decisions, which, in turn, imparts a higher level of confidence about the adequacy of the clothing selection.
A permeation field test has a variety of applications. As haz-mat teams employ a more cautious approach to emergency response, they make greater efforts to assess the situation and the risks associated with the chemicals involved. Applying a permeation field test to this assessment process can only increase the safety of the team. Kit testing of team protective clothing can be extremely valuable in a number of situations including:
- when no data or recommendations for protective clothing exist for the chemicals involved,
- when data or recommendations are not specific to the team’s inventory of protective clothing,
- when data on a protective clothing ensemble or suit are incomplete for spill chemicals (no data on the visor, gloves, or boots),
- when the chemical cannot be readily identified,
- when chemical mixtures are involved, and
- when extreme environmental conditions exist. (High temperatures can have a profound effect on chemical permeation breakthrough times and rates.)
A test kit may also be used to screen clothing before an incident, especially for splash suits and other garments where chemical resistance data may be lacking. Teams knowing of bulk chemicals used within their jurisdiction may prepare before an emergency by qualifying the performance of their protective clothing against these potential spill chemicals.
If properly used, a permeation test can also discriminate performances between different protective garments or clothing items to allow haz-mat teams to buy the least expensive clothing that provides adequate protection. This practice may reduce response costs and eliminate disposal of highly expensive encapsulating suits when a cheaper suit can still offer a safe level of chemical protection.
KIT LIMITATIONS
The methodology of the permeation cup method is not without its limitations. It is not intended to replace the more sophisticated laboratory permeation test. The technique applies mainly to chemical liquids with moderate to high vapor pressures. Some heavy, lowvolatility liquids such as oils or similar substances may permeate but not be detected with the permeation test kit. The sensitivity of the analytical balance will affect how readily material permeation is detected. All field trails of the method have been performed using a two-decimal-place balance. More sensitive balances are available, but these are both costly and often lack field ruggedness. A two-place balance is the best compromise between sensitivity, field durability, and cost.
Use of a kit may also be hampered by the need for emergency action without sufficient time for testing and the dangers in sampling site chemicals. Some response efforts may require immediate action, and waiting for test results would pose an unacceptable delay. Of course, any time teams enter a spill area under such circumstances, they undertake considerable risk and must generally select the best protection available at the time.
There are similar hazards in obtaining the chemical sample for testing materials with the kit. The sample chemical must be brought back to the location where the kit is set up for testing. The people responsible for collecting the sample must also wear the best protective clothing available for this task. All those conducting the test must as a minimum wear eye protection and gloves. Using a respirator may also be appropriate.
Once the permeation resistance of sample materials has been determined, it may be possible to downgrade the level of protection needed as warranted by the test results and haz-mat team criteria.
Selecting economical protective clothing for the emergency responder has become a complex and risky problem. Potential exposure to a variety of chemicals and mixtures, constraints such as the length of time the suit must be worn, the temperature and physical hazards at the scene, absence of data for most garment materials, and budget limitations make it almost impossible to select a protective garment ensemble for every hazardous-chemical incident with any degree of confidence. Most often, haz-mat team leaders must rely on their own experience and judgment to determine the appropriate clothing to wear. Without proper backup data, these hunches could result in increased liability for the department.
Field specific/on-site protective clothing evaluation may be improved by using a permeation field test kit. A field test kit offers quick results and a reliable way to document material performance under field conditions by measuring chemical permeation.
REFERENCES
DOT Emergency Response Guidebook, 1987 Edition.
A.D. Schwope et al., Guidelines for the Selection of Chemical Protective Clothing, 3rd Edition, American Conference of Governmental Industrial Hygienists, Cincinnati, OH, 1987.
L.H. Keith et al., GloveES+, Version 2.2, Radian Corporation, 1989.
S.P. Berardinelli, “Chemical Resistance Field Test Method,” NIOSH Publication, Morgantown, WV, 1985.
S.P. Berardinelli et al., “A Portable Chemical Protective Clothing Test Method: Application at a Chemical Plant,” Am. Ind. Hyg. Assoc. J. (48), pp. 804-808, September 1987.
J.F. Stampher and A.D. Schwope, “Feasibility Study of a Field Test for Chemical Protective Clothing,” Los Alamos National Laboratory Report, Los Alamos, NM, 1985.
T.R. Carroll and A.D. Schwope, “Evaluation, Development, and Verification Networks for Rapid, On-Site Determination of Appropriate Chemical Protective Clothing,” EPA Report, Cincinnati, OH, 1988.