Page 22 - Occupational Health & Safety, August 2018

PROTECTIVE APPAREL
Selecting Chemical-Protective Clothing
Each end-use siCtuation must be evaluated for its particular risks.
BY PAUL DACEY
hoosing the right chemical-protective the material, seams, or suit closures. NFPA 1992 as- clothing can be difficult due to a lack of sociates liquid-tight integrity and penetration data standards and insufficient data. It has been (ASTM F903) with liquid splash protection. Because common to choose chemical-protective clothing of this type is designed to protect the wearer
clothing based on the A, B, and C levels defined by the EPA. While these definitions provide guidelines and a framework for discussing PPE, the descriptive nar- rative in these levels does not identify the minimum performance criteria required to assure that the wear- er is adequately protected from any specific hazards.
The NFPA Approach
Choosing the correct protective clothing requires a clear understanding of what the garment is expected to do and why it is being worn. This practical and sim- ple approach was used by the National Fire Protection Association (NFPA) to establish performance-orient- ed protective clothing standards as follows:
■ NFPA 1991: Vapor-Protective Ensembles for Hazardous Materials Emergencies
■ NFPA 1992: Liquid Splash-Protective Ensem- bles and Clothing for Hazardous Materials Emergencies These standards address full ensemble perfor- mance. Each standard sets minimum levels of per- formance for protection provided by the overall en- semble, garment material, seams, closures, and other components. These criteria have been written with the hazardous chemical emergency response team in mind, but they can apply to a number of other protec-
tive clothing applications as well.
When Vapor Protection is Needed
When you need vapor protection, it is appropriate to choose a certified vapor-protective ensemble when the capability to protect against a specific chemical is based on permeation data (ASTM F739). Permeation is the process by which a chemical moves through material on a molecular level. NFPA 1991 associates vapor-tight integrity and permeation data (ASTM F739) with vapor protection. Therefore, vapor-pro- tective ensembles compliant with NFPA 1991 are suit- able for this purpose.
When Liquid Splash Protection is Needed
When you need liquid splash protection, but do not need vapor protection, it is appropriate to choose a certified liquid splash protective ensemble that meets NFPA 1992. These protective ensembles are selected for their capability to protect against a specific chemi- cal based on penetration data (ASTM F903). Pen- etration is the bulk flow of a liquid chemical through
from liquid contact but allows exposure to vapors,
permeation data is inappropriate for judging material performance for this level of protection.
In addition, the overall ensemble also must dem- onstrate liquid-tight integrity. NFPA 1992 provides test methods and criteria for making this assessment. Organizations such as the Safety Equipment Institute (SEI) and Underwriters Laboratories (UL) will certify complete protective clothing ensembles that meet the NFPA standards.
Other test methods are often used to describe the liquid resistance of materials. However, the choice of liquid splash-protective clothing should be based on the results of penetration testing that has been per- formed in accordance with the procedures in ASTM F903, Procedure C. These criteria provide a truer eval- uation of liquid barrier performance.
When Both Vapor and Liquid Splash Protec- tion Are Needed
When you need both vapor and liquid splash protec- tion, it is appropriate to choose a certified vapor-pro- tective ensemble compliant with NFPA 1991 because, by definition, vapor-protective ensembles also pro- vide liquid splash protection. Never use liquid splash- protective clothing in vapor exposure situations, even if the material offers acceptable resistance to chemical permeation, because these suits lack overall vapor-tight integrity. Penetration data is inappropriate for judging material performance for this level of protection.
Measurement of Penetration Resistance
The penetration test as specified in National Fire Pro- tection Association (NFPA) 19921 measures the resis- tance of protective clothing materials to penetration by liquids using a one-hour, one-sided liquid exposure to the normal outside material surface. The test is con- ducted at atmospheric pressure and room temperature. During the sixth minute, the test is conducted at 2 psig to simulate the pressure from a burst pipe. Liquid pen- etration is detected visually at the end of the test. Pen- etration results are recorded as either “PASS” or “FAIL.”
Heat Stress is Also a Serious Hazard
Heat stress is a serious hazard to wearers of chemical protective clothing. In some cases, heat stress may be even more dangerous than the chemical hazard itself.
18 Occupational Health & Safety | AUGUST 2018
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