Chapter 6 - New Developments at NIOSH

1. Respiratory Physiology

To develop guidelines for workers wearing respirators and associated protective clothing, NIOSH has undertaken several research projects examining physiological response and worker tolerance at a variety of work rates and temperatures. The initial studies examined the effects of wearing four types of clothing/respirator ensembles while the subjects were performing at 30 and 60 percent of their individual aerobic capacity. Thermal, cardiovascular, respiratory, and subjective parameters were measured. Further work has recently been conducted examining responses at 10, 20 and 30 degrees Centigrade. Additional types of protective ensembles have also been studied. Preliminary results show that significant stress occurs with workload and temperature. These factors, as well as type of ensemble should be considered in determining safe work practices.

2. Filtration Mechanics

Research projects are underway and are planned to study the effects of several parameters, such as particle size, particle weight, particle shape, and material, on the efficiency of various filter materials. A study with a lead aerosol indicated that particle weight had no significant effect on filter efficiency. A study of fibrous aerosols is beginning. A filtration study with variably sized latex spheres is nearly complete.

3. Sorption Technology

In addition to conducting tests of MSHA/NIOSH-certified respirator cartridges against a variety of organic vapors, to determine the relation of the service times and resistances to the carbon tetrachloride test now in 30 CFR 11, NIOSH is studying the applicability of the Jonas Kinetic Model for predicting organic vapor permeation. Test data indicate that sorbents tested against carbon tetrachloride have above average service life, in comparison with other organic vapors tested thus far.

4. Quantitative Respirator Efficiency Testing

NIOSH is presently conducting research studies to evaluate published assigned protection factors and to determine the causes of known variability in quantitative fit testing. Quantitative workplace fit tests of powered air-purifying respirators have demonstrated that the previously assigned protection factors for that type of respirator were too high. The lower assigned protection factors for powered air-purifying respirators, prescribed in this publication, reflect this research. A similar study of pressure-demand self-contained breathing apparatus during firefighting operations has been initiated in 1987. NIOSH has determined that several factors variously affect the magnitude of a respirator leak, during quantitative fit testing, both in the laboratory and in workplace studies. The greatest effects have been found to be from leak site and probe location.

5. Certification of New Types of Respirators

Acting in accordance with the authority in 30 CFR 11 Section 11.30 (b), which permits MSHA/NIOSH to certify other types of respirators not described in 30 CFR 11, NIOSH has issued a number of special minimum requirements documents which permit the testing and certification of special respirators. NIOSH issues such requirements only after thorough investigation of the respirators and their use, and after extensive discussion and review by users, regulatory agencies and respirator manufacturers.

Other types of respirators which have been or may be certified under these special requirements include vinyl chloride, formaldehyde and other chemical cartridge respirators, and combination high-efficiency filter and supplied-air respirators.

On November 18, 1985, a Federal Register Notice was published detailing the requirements for certification of positive pressure closed-circuit self-contained breathing apparatus. Basically, there are two types which may be certified: (1) apparatus which use a breathing gas of pure oxygen, and (2) apparatus which use a breathing gas in which the oxygen concentration is not greater than 30 percent by volume. The following requirements, limitations, and cautions apply under present 30 CFR 11 Federal regulations:

Requirements for Certification of Positive-Pressure Closed-Circuit Self-Contained Breathing Apparatus

1. Where the apparatus uses a breathing gas (other than pure oxygen) the breathing gas will be respirable and not contain more than 30 percent by volume of oxygen.
2. The positive pressure closed-circuit self-contained breathing apparatus will meet all applicable requirements of 30 CFR 11 as prescribed for closed-circuit self-contained breathing apparatus, including those designed as demand flow devices.
3. The positive pressure closed-circuit self-contained breathing apparatus will maintain a positive pressure in the facepiece during all pressure and flow tests.

Certification Label Specifications

The following minimum limitations and conditions apply to positive pressure closed-circuit self-contained breathing apparatus and will appear on the certification label for each device:

Limitations

1. Do not use this apparatus where there is direct exposure to open flames or in high radiant heat. (This limitation applies to 100 percent oxygen apparatus only.)
2. Provide proper care, training, and maintenance of the apparatus as specifically described in the manufacturer's instructions and maintenance manuals.
3. After each use of this apparatus, a fully charged breathing gas container and a recharge of carbon dioxide scrubber shall be installed.
4. Thorough cleaning and disinfecting of facepiece, breathing tube, and breathing bag must be done in accordance with the manufacturer's instructions.

Cautions

1. Keep exposed hair to a minimum when using apparatus near open flames or in high radiant heat.
2. A good facepiece seal is important since facepiece leakage will seriously reduce service time.
3. Use of pure oxygen or oxygen enriched air increases flammability and lowers the ignition temperature of most materials.

In addition, presently available information indicates that the use of pure oxygen during direct exposure to open flames and/or high radiant heat should not be permitted. Further, NIOSH has determined that until it has been demonstrated satisfactorily that these devices can be worn safely under such conditions they should be presently limited to use which do not involve exposure to open flames or high radiant heat. Therefore, the oxygen concentration in a mixed gas system is limited to between 23 and 30 percent for use under these conditions. These limitations are based on what is physiologically safe for the necessary oxygen level at the lower end and on the effects of increased oxygen concentrations on both combustion and ignition temperatures at the upper end. These requirements are in addition to those presently listed in 30 CFR 11, both of which must be met by the SCBA prior to certification.

Consequently, when positive pressure closed-circuit breathing apparatus become available as certified devices, then the present closed circuit limitations and recommendations will be expanded to give users more selection guidance for safe application. That is, apparatus selection could become more performance oriented versus design oriented as present considerations and practices require.

6. NIOSH Respirator Problem Investigation

Since July 1, 1982, NIOSH has been investigating reports of problems with MSHA/NIOSH-certified respirators. These reports are from NIOSH audits of certified respirators, and from regulatory agencies and users and manufacturers of respirators. As of August 1, 1987, a total of 215 reports were received. The total includes 15 fatalities of employees who were wearing self-contained breathing apparatus at the time of their deaths.

The goals of the program are to increasingly justify the user's reliance on the MSHA/NIOSH respirator certification program and to indicate to respirator manufacturers that NIOSH is sincere in its desire to increase the safety and reliability of certified respirators.

During the last year of the program, NIOSH has noted that more manufacturers are receiving and directly investigating reports of problems on their own. They are advising NIOSH of the receipt of each problem and are providing NIOSH with follow-up information concerning the investigation and resolution of each problem. NIOSH regards this as an advantageous development, since it promotes more prompt response to and resolution of problems, increases customer satisfaction, and offers the manufacturer opportunities to learn about users' needs and wishes on a first-hand basis.

NIOSH will continue this program and encourages users to contact respirator manufacturers and NIOSH concerning problems with MSHA/NIOSH-certified respirators.

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