Study of surgical face mask products according to criteria for respiratory protective devices

Status:

completed 12/2006

Aims:

Surgical face mask products are used daily in many areas of health care: not only to protect patients, but frequently also for protection of the medical personnel's respiratory tracts against infectious germs originating from the patient. Relevant tests conducted in accordance with standardized requirements are to show whether these products actually provide suitable respiratory protection. Following the emergence of new forms of human pathogen (SARS), a study conducted in 1995 at the BG Institute for Occupational Safety and Health (BGIA) on 11 different types of surgical face mask products was updated in order to describe the current state of the art.

Activities/Methods:

Based upon DIN EN 149, "Filtering half masks to protect against particles - Requirements, testing, marking", three significant tests for assessment of the protective action were conducted in a triple test arrangement on 16 different products, selected at random and typical of those on the market. Besides measurement of the breathing resistance, the total inward leakage and the permeability of the filter material were measured for assessment of the potential ingress of hazardous substances (pathogens). Over 99% of the NaCl particles of the common salt test aerosols employed according to the DIN EN 143 standard, "Filtering half masks to protect against particles - Requirements, testing, marking", are smaller than 1 µm, and approximately 70% are smaller than 0.1 µm. The worst-case range of isolated viruses (approx. 0.01 µm to 0.3 µm) is thus virtually covered, and the range of the highest permeability of such filter media fully covered. The permeability of the filter material at a continuous volume flow rate of 95 l/min represents the worst case, i.e. the probable maximum short-time peak volume flow. The permeability of the filter material measured additionally at a constant volume flow rate of 30 l/min corresponds to the mean value over the inspiration phase of anticipated respiration by the test subjects during light to medium physical activity, and is intended to provide information for estimation of the face leakage, which can be assumed to be approximately equal to the difference between the total inward leakage and the material permeability.

Results:

Following measurement of the total inward leakage, which serves as a measure for the effective protection under standardized wearing conditions, 12 of the 16 products fail even to satisfy the requirements for particle filtering half masks with the lowest protection level FFP1. Four products satisfy the corresponding requirements of respiratory protective devices to DIN EN 149; of these, three have a protection corresponding to that of type FFP1 (max. total leakage 22%), and one corresponding even to that of type FFP3, with a maximum permissible total inward leakage of 2%. Measurement of the filter material permeability at the required volume flow rate of 95 l/min reveals a similar picture. With penetration values of between 22% and 95%, 12 products are outside the range permitted by the standard. Only three face masks satisfy stage FFP1 (max. 22%); one attained the FFP2 performance rating (max. 6%). Altogether, of the four products which satisfied the requirements for the leakage and the four which satisfied those for filter permeability in accordance with the standard, only three were left which satisfied both. The requirements placed by the standard upon the maximum permissible pressure drop across the filter material as an essential contribution to the resistance to inspiration and expiration present no obstacle for the majority of the face mask products.

The results obtained show that the leakage between the mask frame and the wearer's face caused by the gas-tight seat becomes more significant as a component of the total inward leakage with increasing performance of the filter material. In the same way, the influence of the particle size distribution upon the total respiratory protection performance is of decreasing relevance. On products in which the material possesses adequate filtration properties, the leakage between the mask frame and the wearer's face is therefore virtually the sole determining factor. Discussion of the size and type of the particles is irrelevant in this context. The filter resistance of the material, the form and flexibility of a face mask product and its fit are the decisive factors for the leakage between the mask frame and the wearer's face.

Altogether, the updated examination of the medical face mask products against the requirements for respiratory protection confirms the results of the study performed in 1995.

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