Fire Department Self-Contained Breathing Apparatus (SCBA) Program
[NFPA 1404-1996, TIA
Log No. 514, Reference 7-1.1]
CC Austin, G Dussault
The NFPA Technical Committee on Respiratory Protection and Personal Alarm Equipment has proposed that NFPA 1404 (1996) 7-1.1 be revised to read as follows:
Compressed gaseous breathing air for SCBA cylinders shall meet the requirements of ANSI/CGA G-7.1, Commodity Specification for Air, with a minimum air quality of Grade D, and shall have a dew point level of -64oF (-54oC) or drier (24 ppm v/v or less), and a maximum particulate level of 6.5 mg/cu yd (5 mg/m3) air.
We agree that 7-1.1 is in need of revision but we cannot support the above proposal of the Technical Committee. We propose the following revision in its place:
Compressed breathing air shall meet or exceed the requirements of ANSI/CGA G-7.1 (1989), Commodity Specification for Air, with a minimum air quality of Grade G, and shall have a pressure dew point (at line pressure) at least 10oF (5.6oC) below the minimum temperature to which any part of the breathing air system is exposed at any season of the year. Under no circumstances shall the atmospheric dew point of the breathing air exceed -63oF (-53oC) nor shall the maximum levels of oil, particulates and condensates exceed 1 mg/m3, measured at 69.8oF (21oC) and 14.7 psig (101.3 kPa).
Reason:
We have deleted the reference to SCBA cylinders since the same criteria should apply to all compressed breathing air systems used by firefighters, including supplied air systems.
The ANSI/CGA G-7.1 Commodity Specification for Air(1) cautions that the specifications cover the requirements for several grades of air (not necessarily breathing air) which are commercially available for various end uses, and states that it should not be confused with air quality standards, regulations or safety codes. The CAN3-Z180.1-M85 Standard(2) covers the minimum requirements for the purity of compressed breathing air. It differs significantly from the CGA G-7.1 Grades D, E and G air on a number of important criteria, having lower limits for oil, particulates and condensates (1 mg/m3), total hydrocarbons (1/10th of the current TLV), halogenated hydrocarbons (5 ppm), NO2 (0.3 ppm), N2O (2.5 ppm) and methane (25 ppm), but it corresponds more closely to Grade G than to Grade D or Grade E air. It is important to understand that oil-lubricated breathing air compressors, operating at high pressure, produce oil, particulate, water and toxic gas contamination, including carbon monoxide, and that the air produced by these compressors must be processed through an air purification system before it is fit for human respiration. The Montréal Fire Department, in collaboration with McGill University, has conducted a detailed study of compressed breathing air quality(3). The study shows that dangerous contamination of compressed breathing air used by firefighters can and does occur. Furthermore, the results of the study show that when the limits established by the CAN3-Z180.1-M85 Standard are not met, the system is out of control and firefighters may be exposed to unacceptably high levels of toxic contaminants in addition to the risk of breathing apparatus freeze-up in cold weather. Finally, the study shows that operation of compressors and quality control of compressed breathing air meeting the CAN3-Z180.1-M85 Standard are within the technical capabilities of a municipal fire department.
The dew points quoted in the CGA G-7.1 (1989) commodity specifications and in the NFPA 1404 (1996), 1500 (1992) and 1981 (1992) Codes, refer to the quantity of water vapour found in the air, measured at atmospheric pressure. SCBA's typically use line pressures of 2216 psig. To determine the temperature at which water vapour may condense and freeze in the pressure reducing regulator, it is necessary to compare the pressure dew point to the ambient temperature at which the SCBA is used. Conversion tables are included in the CAN3-Z180.1-M85 Standard. For example, the proposed maximum [atmospheric] dew point of -65oF (-54oC), or 24 ppmv of water, corresponds to a pressure dew point in the regulator of +21oF (-6oC), or 3624 ppmv of water at a line pressure of 2216 psig. However, the CGA G-7.1 (1989) and the NFPA 1404 (1996) also require that the [pressure] dew point not exceed 10oF (5.6oC) less than the coldest temperature expected in the area for both Grade D and Grade G air. Thus, an SCBA containing air with a dew point of -65oF (-54oC), measured at atmospheric pressure, could not be used at a line pressure of 2216 psig in areas, such as Alaska, the American Mid-West and New England states, where winter temperatures are less than +31oF (-0.6oC). The maximum allowed pressure dew point of air in an SCBA used at -11oF (-24oC), for example, is -21oF (-31oC), i.e. 10 degrees colder than -11oF, or 347 ppm of water at 2216 psig, corresponding to -95oF (-70.5oC) or 2.3 ppm of water measured at atmospheric pressure.
References
1. ANSI/CGA G-7.1 (1989). Commodity Specification for Air. Compressed Gas Association.
2. CAN3-Z180.1-M85 (1985). Compressed Breathing Air and Systems. Canadian Standards Association.
3. Austin CC., Ecobichon DJ., Dussault G, Tirado C (1997). Carbon monoxide and water vapour contamination of compressed breathing air for firefighters and SCUBA divers. Journal of Toxicology and Environmental Health, In Press.
March 1997
Backed to "Compressed
breathing air" page