Error Analysis in Assessing Respirator Protection Factors

Abstract

Two methods of investigation are presented which can be useful in quantitative industrial hygiene. Propagation of error theory is used to predict the precision of air concentration measurements and to demonstrate the major source of imprecision when measuring aerosols using gravimetric analysis. Predictable precision is shown to vary from ±5 to ±25 percent with the largest proportion of this imprecision changing from the gravimetric measurement of mass at low aerosol concentrations to the control of air sample flow rate at high concentrations. When evaluating workplace protection factors (WPFs), both of these conditions can exist simultaneously as in-mask and ambient concentrations, respectively, and their combined effect is investigated. The use of factor analysis is then demonstrated by investigating the impact of noncompliance with respirator use on WPFs. This impact varies with the level of effective protection (EPF), the fraction of time the wearer is not in compliance, and whether the compliance and noncompliance contaminant concentrations are equal or unequal and differ by a ratio D. For example, noncompliance in a uniform environment for an interval of only 0.02 percent of the total work time will cause a 25 percent bias error between a measured EPF of 1000 and the corresponding WPF had compliance been complete. On the other hand, if the environment of compliance has higher concentration conditions than the environment of noncompliance by a ratio of 5:1, then a 10 percent interval of noncompliance is required to generate this same 25 percent error for a measured EPF of 10. Application of these quantitative tools can greatly aid the efficient allocation of a hygienist's limited time and attention.