Atmosphere-supplying respirators provide protection against oxygen deficiency and toxic atmospheres. The breathing atmosphere is independent of ambient atmospheric conditions. General limitations: Except for some air-line suits, no protection is provided against skin irritation by materials such as ammonia and hydrogen chloride, or against sorption of materials such as hydrogen cyanide, tritium, or organic phosphate pesticides through the skin. Facepieces present special problems to individuals required to wear prescription lenses. Use of atmosphere-supplying respirators in atmospheres immediately dangerous to life or health is limited to specific devices under specified conditions.
- Self-Contained Breathing Apparatus (SCBA) The wearer carries his own breathing atmosphere.
Limitations: The period over which the device will provide protection is limited by the amount of air or oxygen in the apparatus, the ambient atmospheric pressure (service life of open-circuit devices is cut in half by a doubling of the atmospheric pressure), and the type of work being performed. Some SCBA devices have a short service life (less than 15 minutes) and are suitable only for escape (self-rescue) from an irrespirable atmosphere. Chief limitations of SCBA devices are their weight or bulk, or both, limited service life, and the training required for their maintenance and safe use.
- Closed-Circuit SCBA: The closed-circuit operation conserves oxygen and permits longer service life at reduced weight. The negative-pressure type produces a negative pressure in the respiratory-inlet covering during inhalation, and this may permit inward leakage of contaminants; whereas the positive-pressure type always maintains a positive pressure in the respiratory-inlet covering and is less apt to permit inward leakage of contaminants.
- Open-Circuit SCBA: The demand type produces a negative pressure in the respiratory-inlet covering during inhalation, whereas the pressure-demand type maintains a positive pressure in the respiratory-inlet covering during inhalation and is less apt to permit inward leakage of contaminants.
- Supplied-Air Respirators. The respirable air supply is not limited to the quantity the individual can carry, and the devices are lightweight and simple.
Limitations: Limited to use in atmospheres from which the wearer can escape unharmed without the aid of the respirator. The wearer is restricted in movement by the hose and must return to a respirable atmosphere by retracing his route of entry. The hose is subject to being severed or pinched off.
- Hose mask: The hose inlet or blower must be located and secured in a respirable atmosphere.
- Hose mask with blower.
If the blower fails, the unit still provides protection, although a negative pressure exists in the facepiece during inhalation. - Hose mask without blower.
Maximum hose length may restrict application of device.
- Hose mask with blower.
- Air-Line Respirator (Continuous Flow, Demand, and Pressure-Demand Types): The demand type produces a negative pressure in the facepiece on inhalation, whereas continuous-flow and pressure-demand types maintain a positive pressure in the respiratory-inlet covering and are less apt to permit inward leakage of contaminants. Air-line suits may protect against atmospheres that irritate the skin or that may be absorbed through the unbroken skin.
Limitations: Air-line respirators provide no protection if the air supply fails. Some contaminants, such as tritium, may penetrate the material of an air-line suit and limit its effectiveness. Other contaminants, such as fluorine, may react chemically with the material of an air-line suit and damage it.
- Hose mask: The hose inlet or blower must be located and secured in a respirable atmosphere.
- Combination Airline Respirators with Auxiliary Self Contained Air Supply
The auxiliary self-contained air supply on this type of device allows the wearer to escape from a dangerous atmosphere. This device with auxiliary self-contained air supply is approved for escape and may be used for entry when it contains at least a 15-minute auxiliary self-contained air supply.
General limitations: Air-purifying respirators do not protect against oxygen-deficient atmospheres nor against skin irritations, or sorption through the skin of airborne contaminants The maximum contaminant concentration against which an air-purifying respirator will protect is determined by the design efficiency and capability of the cartridge, canister, or filter and the facepiece-to-face seal on the user. For gases and vapors, the maximum concentration for which the air-purifying element is designed is specified by the manufacturer or is listed on labels of cartridges and canisters. Nonpowered air-purifying respirators will not provide the maximum design protection specified unless the facepiece or mouthpiece/nose clamp is carefully fitted to the wearer's face to prevent inward leakage. The time period over which protection is provided is dependent on canister, cartridge, or filter type; concentration of contaminant; humidity levels in the ambient atmosphere; and the wearer's respiratory rate. The proper type of canister, cartridge, or filter must be selected for the particular atmosphere and conditions. Nonpowered air-purifying respirators may cause discomfort due to a noticeable resistance to inhalation. This problem is minimized in powered respirators. Respirator facepieces present special problems to individuals required to wear prescription lenses. These devices do have the advantage of being small, light, and simple in operation. Use of air-purifying respirators in atmospheres immediately dangerous to life or health is limited to specific devices under specific conditions.
- Vapor- and Gas-Removing Respirators
Limitations: No protection is provided against particulate contaminants. A rise in canister or cartridge temperature indicates that a gas or vapor is being removed from the inspired air. An uncomfortably high temperature indicates a high concentration of gas or vapor and requires an immediate return to fresh air.
Use should be avoided in atmospheres where the contaminant(s) lack sufficient warning properties (that is: odor, taste, or irritation at a concentration in air at or above the permissible exposure limit). (Vapor- and gas-removing respirators are not approved for contaminants that lack adequate warning properties). Not for use in atmospheres immediately dangerous to life or health unless the device is a powered-type respirator with escape provisions.- Full Facepiece Respirator: Provides protection against eye irritation in addition to respiratory protection.
- Quarter-Mask and Half-Mask Facepiece Respirator: A fabric covering (facelet) available from some manufacturers shall not be used.
- Mouthpiece Respirator: Shall be used only for escape applications. Mouth breathing prevents detection of contaminant by odor. Nose clamp must be securely in place to prevent nasal breathing. A small lightweight device that can be donned quickly.
- Particulate-Removing Respirators
Limitations: Protection against nonvolatile particles only. No protection against gases and vapors. Not for use in atmospheres immediately dangerous to life or health unless the device is a powered-type respirator with escape provisions.- Full Facepiece Respirator: Provides protection against eye irritation in addition to respiratory protection.
- Quarter-Mask and Half-Mask Facepiece Respirator: A fabric covering (facelet) available from some manufacturers shall not be used unless provided for use with respirator.
- Mouthpiece Respirator: Shall be used only for escape applications. Mouth breathing prevents detection of contaminant by odor. Nose clamp must be securely in place to prevent nasal breathing. A small, lightweight device that can be donned quickly.
- Combination Particulate- and Vapor- and Gas-Removing Respirators
The advantages and disadvantages of the component sections of the combination respirators as described above apply. - Combination Atmosphere-Supplying and Air-Purifying Respirators
The advantages and disadvantages, expressed above, of the mode of operation being used will govern. The mode with the greater limitations (air-purifying mode) will mainly determine the overall capabilities and limitations of the respirator, since the wearer may for some reason fail to change the mode of operation even though conditions would require such a change. Each respirator wearer must complete and submit the ORCBS/Olin respirator wearer questionnaire. This questionnaire will be used for respirator selection purposes/and medical screening information.