Supplied Air/Breathable Gas RPD

Supplied air/breathable gas respiratory protective devices (RPD) contains a means for supplying uncontaminated breathable gas/air to the wearer. This can be achieved by a number of means.

  1. Self-contained RPD provides the highest independence for the wearer mobility by using pressurized breathable gas in valved cylinders or generated by a chemical reaction during use, as an integral part of the RPD e.g. Self-contained breathing apparatus (SCBA)
  2. Other supplied breathable gas RPD use a gas source that is not part of the RPD nor carried by the wearer. The breathable gas can be supplied by a compressor located outside the hazardous area, from pressurized cylinders or from an uncontaminated area by a blower or drawn by the breathing action of the wearer .e.g. air line connected to an air/panel & compressor

Supplied air/breathable gas RPD with emergency breathing device (EBD) is mandated in a number of specific scenarios as below:

  • Oxygen deficient environments
  • Immediately Dangerous to Life & Health (IDLH)
  • Unknown contaminants

These types of RPD are classed/described as below per the nominated standards.

AS/NZS ISO 16973:2023 Supplied Air/Breathable Gas RPD have the following classifications:

  • Sxxxx – Supplied breathable gas RPD that have a fixed volume of breathable gas (self-contained) shall be classified by the volume of breathable gas available for respiration and shall be designated by the letter “S” followed by the gas capacity in liters rounded down to increments of 150 l up to 900 l and increments of 300 l above 900 l. Sxxxx where xxxx is the available breathable gas volume. e.g. Self-contained breathing apparatus (SCBA). For example, if the SCBA available breathable gas capacity is 1260L it would have a classification of S1200. Typical examples of self-contained sources could be breathable gas cylinder, chemical oxygen or liquified-breathable gas.
  • SY – Air supply from an external source e.g. compressor located outside the hazardous area, from pressurized cylinders or from an uncontaminated area by a blower or drawn by the breathing action of the wearer such as an airline connected to an air/panel & compressor

AS/NZS 1715:2009 Section 5.3 provides descriptions and information on the various types/function of Supplied air/breathable gas RPD as summarised below

  • Airline RPD – The air supplied to this type of RPE is pressurized, i.e. it is greater than atmospheric pressure. Air-line RPE could utilize a compressor or compressed gas cylinders. . An air-line respirator may be used in conjunction with an SCBA to guard against air-line failure.
  • Self-contained breathing apparatus (SCBA) – The breathable gas supplied to this type of RPE is pressurized, i.e. it is greater than atmospheric pressure. This apparatus uses cylinders strapped to the user’s body.

The mode of air delivery may be on or a combination of types with some described below

  • Continuous flow – The volume of air supplied is more than that required by the wearer. The pressure inside the facepiece or head covering is greater than that of the immediate environment. The pressure is controlled mainly by the degree of restriction to the escaping air, e.g. facial fit, outlet valve resistance, the presence of a neck bib and shoulder cape or integral jacket or suit.
  • Positive pressure demand – The pressure within the facepiece remains greater than the immediate environment during use. The demand valve opens to supply air to the wearer when the positive pressure inside the facepiece decreases to a preset minimum. This type of system is used with a close fitting facepiece. Both types of demand system may receive air either from a compressed airline or from a self-contained source.

Breathable gas/air RPD Quality 

For supplied breathable gas RPD, the breathable gas/air must be in sufficient quality, quantity and at the required pressure for each wearer. The quality of the breathable gas must be checked regularly by a competent person and records kept. Refer to the following sections of the standards where they detail the recommended air quality requirements

  • SA/NZS TS ISO 16975.1:2023 Section 7.6.4
  • AS/NZS 1715:2009 Appendix A

Both standards (as referenced below) also provide informative guidance for the user and/or purchaser of breathable gas/air supply system. There are various components of an air supply systems that may or may not be required to achieve breathable quality air depending on the requirements of the workplace/environment/application

  • SA/NZS TS ISO 16975.1:2023 Annex E
  • AS/NZS 1715:2009 Appendix F

Limitations of General Supplied air/breathable gas RPD

  • A limitation for self-contained supplied breathable gas RPD is the limited capacity of the breathable gas source. The minimum volume of breathable gas required for the duration of the task needs to be calculated in advance according to the risk assessment. A specific work rate sequence has to be determined, and this will depend upon the expected work profile. With these given work rates and the maximum capacity of the source, the minimum volume of breathable gas required can be calculated and the work task planned accordingly.
  • Supplied breathable gas RPD that rely on a supply of breathable air from a compressor require air at a pressure and volume as specified by the RPD manufacturer.
  • Supplied breathable gas RPD that rely on a supply of breathable air from remote breathable gas cylinders have the same limitations as a self-contained breathable gas source.
  • Where the RPD incorporates a hose (class SY RPD), this may restrict the wearer’s mobility.
  • When performing at high work rates, RPD whose oxygen supply is generated from chemical reactions may have increased inhalation temperatures that may be unacceptably high for some wearers.

For example, if entry into the hazardous area requires movement over several meters, movement between floors or levels within a building or transit through very small openings or tunnels/ducts using ladders or crossing railroad tracks, then class SY/Airline RPD may not be suitable because of the possibility of tangling or severing the supplied air hoses. The maximum length of hose permitted by standards may also limit the travel distance of airline respirator wearers. Also, when using class S or combination class SY/S, the distance from the hazardous area to the nearest staging area containing a breathable atmosphere should be known to ensure that the RPD selected will have an adequate supply of breathable gas or that the service life of the auxiliary escape cylinder of the combination class SY/S is adequate for emergency escape.

Particular care should be taken in choosing an air-line or air-hose intended to be used in temperature extremes, or likely to come in contact with solvents or other deleterious materials Solvents may permeate certain types of hose material or destroy them. Heat may also cause the release of objectionable odours into the hose.

Limitations of Supplied air/breathable gas RPD in IDLH atmospheres

  • Where supplied-air RPE is used in IDLH situations, it is essential that training maintenance, inspection procedures and other suitable systems are in place to minimize the consequence of failure of the air supply.
  • Training and supervision of wearers should include removal of devices, use of the EBD and removal procedures to adequately protect others and the environment.
  • In any instance of failure of the air supply wearers may be exposed to full ambient contaminant concentration unless a suitable EBD is incorporated and correctly used. In addition, if decontamination procedures cannot be followed during removal and escape, wearers and others may be exposed to contaminants, and the environment may be contaminated.

Reference/s for further information and detail:

  • AS/NZS 1715:2009 – Selection, use and maintenance – Section 4.3.3, Appendix A, Appendix F
  • SA/SNZ TS ISO 16975.1:2023 – Selection, use and maintenance – Annex A, Annex E