MEASUREMENT OF THE DEGREE OF PROTECTION AFFORDED BY RESPIRATORY PROTECTIVE EQUIPMENT AGAINST MICROBIOLOGICAL AEROSOLS

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1 PII: S0003-^878(96) Ann. occup. Hyg., Vol. 41, Supplement 1, pp , 1997 British Occupational Hygiene Society Crown Copyright 1997 Published by Elsevier Science Ltd Printed in Great Britain 0003-^878/97 $ Inhaled Particles VIII MEASUREMENT OF THE DEGREE OF PROTECTION AFFORDED BY RESPIRATORY PROTECTIVE EQUIPMENT AGAINST MICROBIOLOGICAL AEROSOLS A. C. Redmayne, D. Wake, R. C. Brown and B. Crook Health and Safety Laboratory, HSL, Rill Robens Building, Broad Lane, Sheffield S3 7HQ, U.K. INTRODUCTION Biological aerosols may include viable and non-viable intact microbial cells or cell components, exposure to which may cause respiratory infection, allergic lung disease or toxicosis. Respiratory protective equipment (RPE) is used widely in industry to reduce occupational exposure to a range of substances, including microbiological aerosols. Consequently, there is a need to be able to measure the performance of RPE against microbiological aerosols. This paper describes a series of tests to evaluate the performance of a range of RPE when challenged with bacterial and bacteriophage aerosols. METHODS Microbiological aerosols (bioaerosol) Three bacterial species and a bacteriophage were used to provide a bioaerosol challenge. Pseudomonas alcaligenes [National Collection of Type Cultures No. (NCTC) 10367] are Gram-negative, motile, non-sporulating rods, 0.5 urn in width and between urn in length. They are similar in morphology to Legionella pneumophila, for which they may be considered as surrogates. Bacillus subtilis sub species globigii (NCTC 73) are Gram-positive, nonmotile, sporulating rods. They are urn in diameter and um in length and usually occur in single cells. Micrococcus luteus (NCTC 4351) are Gram-positive, non-motile, nonsporulating cocci occurring in tetrads. Individual cocci are urn in diameter. The bacteriophage used was Tl coliphage wild type, American type culture collection (ATCC) No 11303B1, which has a long slender tail of 150 nm and an hexagonal head 60 nm in length (Harstad, 1965). The host bacterium is Escherichia coli, ATCC Aerosols were generated from aqueous suspensions of each viable organism as described below. Test apparatus. This comprised a wind tunnel with a working section approximately 3 m in length, 1 m in height and 0.6 m in width to provide an enclosed region, maintained at negative air pressure. Within this, bacterial aerosols were generated into a perspex plenum chamber from three medical nebulisers connected 636

2 Degree of protection afforded by respiratory protective equipment 637 in parallel via a manifold to a compressed air supply. Alternatively, a Collison atomiser was used to generate bacteriophage aerosol, as it produces a smaller primary droplet than the medical nebuliser. To challenge RPE filter material with bioaerosol, the filter under test was housed in one of two aerodynamically identical flow lines from the plenum chamber. The other flow line provided an un-filtered reference line for comparison. Perspex boxes connected with tubing to the end of these flow lines each housed an all glass impinger (AGI-30; Cox, 1987), into which the bioaerosol was collected into liquid at an air flow rate of 12.5 l.min" 1. The suspension was used to inoculate agar plates, from which the number of colony or plaque forming units per ml of AGI 30 collection fluid was calculated. The penetration through the or filter was obtained from the quotient of the count per ml passing through the filter compared to that passing through the reference line. Non biological aerosols. The monodisperse urea aerosol tests were carried out using the automated Berglund-Liu test system (Wake, 1995) with particles of 1.5, 3,5,7 and 9 um geometric diameter. The BS 4400 sodium chloride aerosol has an approximate mass median diameter of 0.6 \im and number median diameter of 0.06 fxm. The procedure for carrying out both types of test has been described previously (Wake and Brown, 1988). of a range offilters and surgical s. A wide range of filters for full and half face respirators were tested along with a selection of available disposable nuisance dust s and disposable surgical s. Leakage of s. Although many of the devices showed acceptable filtration efficiency, in order to be useful in practice it is necessary that the extent of face-seal leakage should also be acceptable. To test the effect of face-seal leakage, the test system described above was modified to test a full-face respirator. The twin aerosol flow lines were replaced by a perspex chamber which accommodated the "Sheffield" manikin head wearing a respirator. Aerosol entering the chamber could pass either through the respirator and head or through the reference line. A full face respirator was fitted with a dust filter element (filter code C) which was shown to allow % of an aerosol of M. luteus to penetrate, and % of a sodium chloride aerosol and the respirator was fitted to the "Sheffield" head and then sealed on to the face to prevent unwanted leakage. To provide known leaks, five capillary tubes of different diameter were positioned on the left side of the head between the seal of the and the upper cheek. The assembly was sealed to the and head. All the capillaries were sealed and a penetration test at an air flow rate of 30 l.min" 1 was carried out. Each capillary in turn, starting with the one of largest bore, was opened and the sodium chloride aerosol test repeated until tests had been carried out with all five opened. These tests were repeated with an aerosol of M. luteus. RESULTS AND DISCUSSION Results of penetration of filter material The results are given in Tables 1 and 2. It can be seen that the expected high performance of the more efficient respirator filters was confirmed against both types of aerosol. The poor performance of nuisance dust s previously

3 638 A. C. Redmayne et al. Table 1. of microbiological aerosols through filters Filter code Filter type Ps. alcaligenes B. subtilis M. luteus A B C D E F G H I J K L M N O Merino wool Resin-wool Nuisance dust Resuscitation < * < * < * < * < * < * < * < * < * < * < < < < < < < * No organisms were detected during the counting procedure with the filtered aerosol. observed with non-biological aerosols (Wake and Brown, 1988) was also apparent with bacterial aerosols. For example, the nuisance dust (code J) failed to retain a measurable number of an aerosol of Ps. alcaligenes and allowed up to 79% of B. subtilis to penetrate. Mask L was by far the worst surgical tested, its performance being similar to that of the nuisance dust J, which in appearance is closely resembled. K was also poor; up to % of M. luteus penetrated the material and up to 25.4% penetration of Ps. alcaligenes (Table 1) and up to 78% of NaCl aerosol (Table 2). The two surgical s M and N, that were thought to contain electrostatically charged filter material, performed better. Although it is acknowledged that such s do not classify as respiratory protective equipment, it is probable that they are being used widely in health care as a perceived protection of workers against possible airborne infectious agents from patients. The protection that these s may confer should not be over-estimated.

4 Degree of protection afforded by respiratory protective equipment 639 Table 2. of monodisperse urea aerosols and BS 4400 sodium chloride aerosols through filters Filter code Filter type 1.5 Jim Urea aerosol[ 3 urn 5 um 7 urn 9 urn NaCl aerosol Pen. A B C D E F G H I J K L M N O Merino wool Resin wool Nuisance dust Resuscitation The use of s with a range of efficiencies enabled a comparison to be made between the penetrations of live bacterial aerosols and those of urea aerosols with a defined geometrical diameter, as in previous work (Wake etal., 1992). The results obtained suggested that Ps. alcaligenes behaved as a particle of diameter 1.5 xm or less, B. subtilis behaved as 3-5 \xm and M. luteus as im. The results of the bacteriophage aerosol penetration confirmed the large differences in performance between filter cartridge material, with low penetration and disposable dust -type material with much greater penetration, up to 90% and greater than in some instances. On the whole, penetration of bacteriophage through dust filter material was greater than that of M. luteus, which in turn was greater than that of B. subtilis. More BS 4400 sodium chloride aerosol penetrated the s than did bacteriophage. This would place the effective particle size of the bacteriophage at smaller than bacteria but greater than sodium chloride. Results of known leakage in a full face respirator The results are given in Table 3. The penetration of both bacterial and sodium chloride aerosol increased with the size of leak. The observed penetration of bacteria was greater than that of the sodium chloride aerosol, which was surprising since the sodium chloride particles are smaller than the bacteria, but in general the penetrations of the two aerosols were comparable. The results provided quantifiable evidence of the influence of face seal leakage on RPE performance.

5 640 A. C. Redmayne et al. Table 3. of aerosols through known leakage in a full face respirator Aerosol type BS4400 Sodium chloride Micrococcus luteus Leak size drop drop (mm 2 ) (Pa) (Pa) No leak CONCLUSIONS It can be seen from the results that, generally, biological aerosols behave in a similar way to non-biological aerosols of a corresponding aerodynamic diameter. It can also be concluded that the performance of high efficiency respirator filters can be compromised by poor fit of RPE to the face. REFERENCES BS 4400 (1969) Method for sodium chloride particulate tests for respirator filters. British Standards Institution, London. Cox, C. S. (1987) The Aerobiological Pathway of Microorganisms, pp Wiley, New York. Harstad, J. D. (1965) Sampling submicron Tl bacteriophage aerosols. Appl. Microbiol. 13 (6), Wake, D. (1995) An automated system for measuring the penetration of aerosols through filters. J. Aerosol Sci. 26 (5), Wake, D. and Brown, R. C. (1988) Measurements of the filtration efficiency of nuisance dust respirators against respirable and non-respirable aerosols. Ann. occup. Hyg. 32, Wake, D., Brown, R. C, Trottier, R. A. and Liu, Y. (1992) Measurements of the efficiency of respirator filters and filtering s against radon daughter aerosols. Ann. occup. Hyg. 36,