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Procedures for Testing & Certifying Air-Purifying/Particulate Respirators

Procedures for testing and certifying air-purifying and particulate respirators changed under a final regulation published June 8, 1995 by the National Institute for Occupational Safety and Health (NIOSH). This new standard, called 42 CFR 84, replaces MSHA regulation designated 30 CFR 11 which is based upon testing methods and filtration theory that are more than 20 years old. This action by NIOSH is the first of a series of modules that will incrementally revise current approval requirements for all respirators.

The rule revises test requirements for particulate filter respirators and prefilters for gas and vapor . It establishes new performance criteria for particulate-filter, air-purifying respirators, which are the most widely used types of respirators. They are commonly used for protection against hazardous particulates generated during operations such as:

Welding	Sanding
Grinding	Chipping
Painting	Pesticide Spraying

The certification requirements established with 42 CFR 84 is significant because it will eliminate classification of respirator filters and prefilters by hazard type (ie. dust, mist, fume, etc.), and replaces it with three series of filters which will be classified based on the filter efficiency. There are a variety of factors influencing filter efficiency, many of which are human variables such as leakage from improperly maintained respirators. NIOSH decided to tackle filter efficiency as its primary test criteria because it is an area which can be controlled.

Background

Prior to 42 CFR 84, the rules and procedures for approval of respiratory protective devices were found in 30 CFR 11. These rules have evolved from rules and procedures developed by the U.S. Department of Interior, Bureau of Mines (BOM). Until 1972, BOM was solely responsible for testing and approving respirators. In 1972, 30 CFR 11 was published jointly by the BOM and NIOSH. Over time, BOM’s responsibilities for respirator testing and approval were transferred to the Mine Safety and Health Administration (MSHA). 42 CFR 84 includes provisions to transfer the requirements for approval of respirators from MSHA to NIOSH, and transfers responsibility for certifying most respirators to NIOSH. NIOSH and MSHA will continue to jointly review and approve respirators used for mine rescue and other mine emergencies. In addition, MSHA will continue to test electrical and electronic components of respirators for use in potentially explosive atmospheres in gassy underground mines and issue a separate approval under 30 CFR Part 18 for such respirator components.

Transition Period

NIOSH is allowing three years for the phasing out of CFR 11 approved particulate respirators. As of the effective date of 42 CFR 84 (July 10, 1998), NIOSH will no longer accept applications for new approvals or extensions of approval under 30 CFR 11. All applications received after the effective date of part 84 will be tested to the provisions of 42 CFR 84. A subpart KK containing part 11 requirements for particulate respirators has been added to the part 84 final rule to provide for extensions of approvals needed to address respirator recall and retrofit matters that are associated with health and safety issues for workers. Respirators listed as certified under the provisions of 30 CFR 11, subparts K (particulate respirators), or M (pesticide respirators), may not be sold or shipped by the approval holder as NIOSH/MSHA certified respirators effective July 10, 1998. However, continued use of particulate respirators is under the jurisdiction of the Occupational Safety and Health Administration (OSHA) and MSHA, and therefore is not affected by this rule. Because certifications will not be revoked for 30 CFR 11, NIOSH expects that OSHA and MSHA will permit the continued use of part 11 respirators sold and shipped from existing inventories.

Filter Classification

This rule establishes three series of filters; N, R, and P. Each series has three levels of filter efficiency; 95%, 99%, and 99.7% respectively. The new filter efficiency criterion are the minimum efficiencies to be demonstrated by each filter. The nine classes of filters are outlined in Figure 1, below.

Figure 1. Minimum Filter Efficiency Criteria

* May have a time use restriction on this filter series when oil aerosols are present. DOP = Dioctyl Phthalate NaCl = Sodium Chloride

There have been some questions related to how the new filter efficiency tests reflect conditions commonly encountered in the workplace. 42 CFR 84 tests use a particle size of 3µm which is considered the "most penetrating" particle size range for respirator filters. This "severe environment" subjects the filters to "worst case" tests. The following section describes some of the methods employed in particulate filters to "screen" particles of various sizes, and keep them from penetrating the respirator filter.

Particulate Filtration Theory

Respiratory filtration works to remove inhalable particles of a variety of sizes. It is this range of particulate sizes against which respiratory protection particulate filters are expected to perform. Since the human body "breathing apparatus" is not an efficient filter, many of the particles entering the lungs are captured there, depending largely on the particle’s physical characteristics (diameter, weight, etc.). Subsequently, respiratory protection assists the human apparatus by capturing most of the particles within the filter media prior to entering the breathing zone.

The most common respiratory filters contain pore sizes many times greater than the particles to be removed. The main filtration mechanisms take into account how particles behave in moving airstreams, and place obstacles in the path of moving particles thus resulting in capture of the particle in the filter. In air, combinations of capture mechanisms occur at different flowrates and particle sizes. Each of these capture mechanisms and their combinations make up the effective means by which most particulate respirator filters work.

Interception - Figure 2. Interception is the only capture mechanism in which particles do not deviate from their original streamline paths. As the streamlines approach a filter fiber, they split and compress as they go around the fiber and rejoin of the other side. If a particle moving along these streamlines comes within one particle radius of the surface of the fiber, it is captured. As particle size increases and occupies more than one streamline, capture becomes more probable.

Sedimentation - Figure 3. Sedimentation affects only large particles (2 µm or above), and is a contributor to capture efficiency only at low flowrates. The particle in this scenario is affected by gravity, and crosses the streamlines to be captured by the fiber.

Inertial Impaction - Figure 4. When a particle with sufficient inertia encounters an abrupt change in streamline direction, it will cross the streamlines and impact into the filter fiber. The inertia of the particle depends primarily on its size, density and speed.

Diffusion - Figure 5. Smaller particles are in constant motion, due to bombardment by air molecules. the particles can randomly cross the streamlines, and their probability of touching the filter fiber as they pass is greatly enhanced as their diffusive activity increases. This random motion of particle is dependent on its size and the temperature of the air. Its chances of capture are greatly enhanced by a high residence time near a fiber (low flow rates) and the availability of fibers in its path

Combinations - The sum total of possible capture mechanisms and their interactions also result in efficient particle filtration. For a large heavy particle, the combination of inertial impaction and interception is important. For a large, light particle, diffusion and direct interception are important. If each total capture mechanism is calculated to determine its degree of contribution to capture, then a theoretical sum total filtration efficiency may be determined.

Figure 2. Interception Capture Mechanism

Figure 3. Sedimentation Capture Mechanism

Figure 4. Impaction Capture Mechanism

Figure 5. Diffusion Capture Mechanism

Test Requirements

The new certification tests use the most penetrating aerosol size, 0.3 µm aerodynamic mass median diameter, of either a mildly degrading particulate such as sodium chloride (NaCl), or a highly degrading oil such as Dioctyl Phthalate (DOP). The efficiency of the filter shall be monitored and recorded throughout the test period.

The N- series respirators will be tested to a maximum loading level of 200 mg NaCl per respirator. The minimum efficiency for the filters tested must be equal to or greater than the filter efficiency criterion for the filter class which approval is sought. For example, after being loaded with 200 mg of NaCl, an N95 particulate filter must demonstrate filter efficiencies greater than or equal to 95%. Prior to filter efficiency testing of N-series filters, the filters shall be taken out of their packaging and placed in an environment of 85 + 5% relative humidity at 38 + 2.5° C for 25 + 1 hours. This requirement addresses the effect of humidity on the filter’s efficiency because the NaCl aerosol is less severe than DOP in reducing filter efficiency.

The R- series respirators will be tested to a maximum loading of 200 mg DOP per respirator. The minimum efficiency for the filters tested must be equal to or greater than the filter efficiency criterion for the filter class for which approval is sought.

For P- series filters, if the filter efficiency is decreasing when the 200 mg of DOP challenge point is reached, the test shall be continued until there is no further decrease in efficiency. The minimum efficiency for the filters tested must be equal to or greater than the filter efficiency criterion for the filter class for which approval is sought.

Airflow resistance tests were modified from 30 CFR 11 by deleting the final inhalation resistance requirements. The airflow resistance through the filter is not determined after the loading tests. According to NIOSH, this is because the filter efficiency tests are not designed to simulate loading of the filter at the worksite. Therefore, final inhalation test requirements are not appropriate with the introduction of these new tests. [At 10 times the PEL for lead, assuming a moderate breathing rate of 10 M³ per 8 hour day for a worker, it would take 40 days for a respirator to become loaded with 200 mg of lead.]

Respirator Limitations & Use

Since filter classification of N, R, and P does not provide information as to where to use a specific filter, NIOSH plans to issue a Users Notice or Guide to explain the use of respirators certified under 42 CFR 84. This guide is anticipated to be either an update or supplement to the NIOSH Respirator Decision Logic. Thus, it would not be a legal document as published in the Federal Register. It would be published as a NIOSH recommendation. OSHA and MSHA regulate the actual use of all respirators in the workplace.

Respirators certified according to 42 CFR 84, subpart K, are designed and limited for use as respiratory protection against atmospheres with particulate contaminants that are not immediately dangerous to life or health (IDLH) and that contain adequate oxygen to support life. The N- series filters are restricted to use in those workplaces free of oil aerosols. The R- and P- series filters are intended for removal of any particulate that includes oil-based liquid particles.

Use of Particulate Respirators for Protection Against TB

All nine classes of particulate respirators to be certified under the provisions for the new particulate filter tests (filter efficiency) in part 84 meet or exceed the performance recommendations contained in the CDC "Guidelines for Preventing the Transmission of Mycobacterium tuberculosis in Health-Care Facilities, 1994". According to NIOSH, it is not necessary to subject filter respirators to a bioaerosol as a condition of certification. By using test aerosols of the most penetrating size range as required in part 84, the efficiency-level determination of the certification testing will be the lowest obtainable for any size aerosol. Therefore, the efficiency level against any bioaerosol for any certified respirator will meet or exceed the certified efficiency level. [OSHA regulates the use of respirators in health-care facilities and at this time OSHA still requires HEPA filter respirators to be used.]

Powered Air-Purifying Particulate Respirators

Filters for powered air-purifying respirators (PAPRs) are not affected under the changes to 42 CFR 84. The requirements for PAPRs will be addressed in a forthcoming module. In the interim, powered air-purifying particulate respirators equipped with HEPA filters will be approved under the provisions of 42 CFR 84 subpart KK. Approvals of new PAPRs for particles will only be certified with high efficiency (HEPA) filters as tested under 30 CFR 11. New approvals for PAPRs with dust/mist or dust/fume/mist filters will not be granted.

Pesticide Respirators

The requirements for pesticide respirators from 30 CFR 11 were not included in 42 CFR 84. This rule eliminates the pesticide respirator category and the tests specific to these respirators. Pesticide respirators certified under 30 CFR 11 may not be sold or shipped by the approval holder as NIOSH/MSHA certified respirators after July 10, 1998. These respirators are subjected to the same requirements discussed previously under "Transition Period".

Paint Spray Respirators

The test requirements specific to paint spray respirators are also eliminated under 42 CFR 84. Filters used in conjunction with chemical cartridges, including those that might be used for spray paint will be tested under the same provisions as particulate respirators.

Combination Gas Masks

Combination gas masks are respirators using a canister containing filters for protection against particles in combination with gases, vapors, or gases and vapors. The filters in these devices shall also comply with the requirements of the new part 84 particulate filters except for the airflow resistance test. Airflow resistance requirements of 30 CFR 11 apply as incorporated into 42 CFR 84.

Other Implications

The new certification requirements will also affect other aspects of established Respiratory Protection Programs, including workplace air sampling, respirator selection, fit-testing and training. For these reasons, those responsible for managing respiratory safety programs should seek professional guidance from industrial hygienists, safety professionals and other knowledgeable personnel to aid in selecting the most appropriate respirators and implement acceptable training programs.

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