Minimizing the Effect of Dermal Absorption and Transport of Optimal Chemical Vapors for Simulated Measurement of Workplace Protection Factors (WPF) of Respiratory Protective Equipment
Open Access
- Author:
- Mcwhorter, Heather Fennessey
- Graduate Program:
- Energy and Mineral Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- September 24, 2018
- Committee Members:
- Sarma V Pisupati, Thesis Advisor/Co-Advisor
Jeremy Michael Gernand, Committee Member
Mark Stephen Klima, Committee Member - Keywords:
- respirator
dermal permeability
WPF
ethyl bromide
workplace protection factor - Abstract:
- Understanding the performance of respiratory protective equipment while in use in the workplace is important for ensuring worker protection. When respirator effectiveness measurement occurs in the workplace, the respirator is assigned a workplace protection factor (WPF). WPF is a ratio of the airborne ambient concentration of a substance as compared to the concentration of a substance in a respirator mask. U.S. Occupational Safety and Health Administration (OSHA) uses WPFs to statistically establish assigned protection factors (APFs), which are regulatory and assigned based on classes of respirators. WPF measurements are also made as part of workplace respiratory protection programs to ensure that respirators are properly functioning under workplace conditions. However, little research has been performed to document WPF performance of respirators. In controlled laboratory settings, testing is referred to as simulated WPF (SWPF) testing. In order to identify ideal substances for SWPF testing, a methodology was established to screen substances with published dermal permeability coefficients (Kp). Dermal permeability is of particular interest because if workers do not have chemical resistant clothing covering their entire body, the substance may absorb through the skin, transport through the body, be exhaled by the lungs into the respirator mask, and therefore skew the results of the SWPF testing. To determine which substances should be focused on in future research, almost three hundred substances were evaluated and screened based on health and safety considerations (carcinogenicity, worker occupational exposure limits, and flammability) and laboratory testing considerations (analytic sensitivity, environmental and economic considerations for banned or controlled ozone depleting substances, transport characteristics, and vapor pressure and solubility) to determine ideal substances for SWPF testing. Five substances were identified as a result of the screening for dermal transport modeling including ethyl bromide (CAS 74-96-4), phenanthrene (CAS 85-01-8), cyclohexanol (CAS 108 93-0), cyclohexanone (CAS 108-94-1), and 4-hydroxy-4-methyl-2-pentanone (CAS 123-42-2). Dermal transport characteristics, such as the total amount of a substance absorbed and stratum corneum lagtime as the substance transports from skin into the blood, were determined. Ethyl bromide and phenanthrene were found to perform as well as or better than benchmark substances that have been used in the past used for modeling and SWPF testing, with low dermal absorption and protection by respiratory protection equipment. However, they have lower stratum corneum lagtimes, indicating faster absorption through skin. Phenanthrene laboratory testing also requires lower testing temperature (20°C) due to its saturation vapor pressure. This research concluded that some screened substances can be used as safer alternatives with similar performance for future SWPF testing. Benchmark substances identified are known or reasonably anticipated carcinogens and some have flammability concerns. The five screened substances reduce these health and safety concerns. One substance, ethyl bromide, consistently performed as well as or better than benchmark substances with a minimal dermally absorbed quantity during an 8-hour exposure. Physiologically based pharmacokinetic (PBPK) modeling to determine the exhaled concentration of the screened substances as a result of dermal absorption is recommended. Ethyl bromide is recommended for SWPF testing as a safer, viable option for measuring respirator performance.