Respirators...Selection Must be Based in Identified Atmospheric Hazards
by Adam Schupp
The Respiratory Protection Standard, 29 CFR 1910. 134 (www.sha-slc.gov/OshStd_data/1910_0134 .html) requires that respirator selection be based on the identified atmospheric hazards to which a confined space entrant may be exposed.
There are three general categories of respirators:
>Air-purifying.
>Air-supplying.
>Self-contained breathing apparatus (SCBA).
Air-Purifying Respirators
This type of respirator can be mechanical filter, chemical cartridge, a combination of the two, or a gas mask.
Mechanical filter respirators provide protection against dusts, mists, metal fumes, and smoke. However, they may not provide protection from gasses, vapors, or oxygen deficiency.
The filter traps particulate matter as air is inhaled, but a high-efficiency filter is needed to trap smaller particles.
Chemical cartridge respirators offer protection against intermittent exposure to light concentrations of gases and vapors.
They cannot be used in immediate danger to life or health (IDLH) atmospheres.
Follow these �do-nots� for chemical cartridge respirators:
� Do not use for protection against gaseous material that is extremely toxic in small concentrations.
� Do not use for exposures to harmful gaseous material that cannot be clearly detected by odor.
� Do not use against gaseous material in concentrations that are highly irritating to the eyes, without satisfactory eye protection.
� Do not use for protection against gaseous material that is not effectively stopped by the chemical filter used, regardless of concentration.
Combination mechanical filter/chemical cartridge respirators afford protection against dust, fumes, and mist, with a chemical cartridge for dual or multiple exposure.
Gas masks afford protection against certain gases, vapors and particulate matter, but don�t supply oxygen. They are approved for escape only from IDLH atmospheres and never for entry into such environments.
Gas masks are generally suitable for ventilated areas not subject to rapid change in air-contaminant levels.
Powered air-purifying respirators protect against particulates, gases, and vapors. The air-purifying element may be a filter, chemical cartridge, combination filter and chemical cartridge, or canister.
This type of respirator uses a battery pack power source to operate a blower that passes air across the air cleaning element to supply air to a respiratory inlet covering.
Powered air-purifying respirators generally offer very good protection because they supply air at positive pressure, and leakage is usually outward from the facepiece.
Be aware, however, that high work rates can create a negative pressure in the face piece.
Disposable dusk masks (respirators) offer protection against particulate matter, but the quality of protection is questionable. They cannot be used in an oxygen-deficient environment.
Atmosphere/Air-Supplying Respirators
This type of respirator provides a respirable atmosphere to the wearer, independent of the ambient air.
There are three groups: supplied air, SCBA, and combination SCBA and supplied air.
Type A supplied-air respirators are known as a hose mask with blower. The air is supplied by a motor-driven or hand-operated blower through a strong, large-diameter hose.
The maximum allowed length is 300 feet, which allows the wearer to continue to breathe through the hose if the blower fails.
Type B supplied-air respirator is a hose mask without the blower. The wearer draws air through the hose by inhaling. The maximum length is 75 feet.
Type C supplied-air respirators are known as air lines. The respirator is connected to a suitable compressed air source by a small-diameter air hose.
The quality of air must conform to Grade D Compressed Gas Associations�s Standard CGA G7 1-73, Commodity Specification for Air, 1973.
Type C supplied-air respirators come in three types:
� Constant flow unit, which has a regulated amount of air fed to the face piece. There must be an ample supply of air available. Each device must have an approved pressure range and a maximum of 300 feet of air hose.
� Demand-flow types deliver air flow only during inhalation. The air supply is usually a high-pressure compressed air cylinder, which requires a regulator to control pressure for breathing.
� Pressure-demand flow is a good choice where any inward leakage is unacceptable. It provides positive pressure during both inhaling and exhaling.
SCBA respirators provide complete protection against airborne toxicity and/or oxygen deficiency.
There are five basic types:
� Oxygen cylinder rebreathing SCBAs are equipped with a small cylinder of compressed oxygen, reducing and regulating values, a breathing bag, facepiece, and chemical container to remove carbon dioxide from exhaled air.
The cylinders are approved for 45 minutes, 60 minutes, 2 hours, 3 hours, or 4 hours.
� Demand type SCBA air is provided by a high-pressure air cylinder and airflow is provided on inhalation demand. This is a good escape device from potentially toxic atmospheres that may go beyond the capacity of a gas mask.
� Pressure demand SCBA respirators use the same principle as the pressure-demand air line respirator. They are approved for use where the toxicity is such that the potential face piece leakage of demand apparatus is not tolerable.
� Self-generating SCBAs have a chemical canister that evolves oxygen and removes the exhaled carbon dioxide in accordance with breathing requirements of the wearer.
It eliminates high-pressure cylinders, regulating valves, and other mechanical components. These units are simple to use and don�t require as much regular maintenance.
Combination SCBA and Type C supplied air respirators are an air line respirator with an auxiliary self-contained air supply. They can be used in IDLH atmospheres and the user can switch to the auxiliary air supply if the primary supply fails.
IDLH Factors
Two factors are necessary in establishing IDLH concentrations:
1. The worker must be able to escape within 30 minutes, the maximum permissible exposure time established by OSHA, without losing life or suffering permanent health damage.
2. The worker must be able to escape without severe eye or respiratory irritation or other reactions that could inhibit escape.
Concentrations above IDLH levels require a highly reliable respirator, such as a pressure demand SCBA.
Any situation-approved respirator may be used up to the IDLH level as long as the maximum use concentration, or the limit on the air purifying element, are not exceeded.
IDLH limits can be determined from any certified industrial hygienist, the respirator supplier, AIHA Hygienic Guide or the NIOSH Pocket Guide to Chemical Hazards (www.cdc.gov/niosh/npg/npg.html.)
Adam Schupp is a safety consultant, North Fort Myers, FL; 941-731-5947.
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