Diver's

Education &

Equipment, Inc

18 April 1997

Compressed Gas Association, Inc.

Attn: Mr. Chet Roberts, Technical Manager

Crystal Square 2, Suite 1004

1725 Jefferson Davis Highway

Arlington, VA 22202-4102

Dear Mr. Roberts,

As you and I have discussed by telephone, I am proposing that the Compressed Gas Association, Inc. (CGA) Task Force for revision of CGA Pamphlet G-7.1 American National Standard Commodity Specification for Air revise the maximum level of carbon dioxide (CO₂) from 500 to 1000 parts per million (ppm) for breathing air Grade E. Grade E air, specifically diving air, poses an unnecessarily rigid restriction by limiting carbon dioxide content to 500 ppm. It is a level without physiological justification and which is on occasion difficult to achieve. The following presents my rational with supporting documentation justifying such a change in the CGA standard.

I am part owner of a retail SCUBA diving store (D.E.E.P., Inc.) in Galveston, Texas and a Marine Biologist and Diving Safety Officer for a private research company (LGL Ecological Research Associates, Inc.) of Bryan, Texas. D.E.E.P., Inc. holds the rating of Five Star Training Facility from the Professional Association of Diving Instructors (PAl3I). PADI selected the CGA Grade E standard for quarterly compressor air analyses required of its Five Star Training Facilities. I and others have had difficulty complying with the CO₂ level of Grade E standards, and in fact excessive CO₂ is the most common reason for failure to meet that standard (Ochoa, 1994; see Attachment E).

Current U.S. Navy (USN) and National Oceanic & Atmospheric Administration (NOAA) diving manuals which are used as guides for much of the diving in this country (USN 1988, NOAA 1991) and U,S. Federal Regulations pertaining to commercial diving (29 CFR Part 1910 OSHA and 46 CFR Part 197 USCG) all set the maximum carbon dioxide content at 1000 ppm (0.l0 %) for diving with air (see Attachments C, D, E and F). Some earlier editions of USA diving manuals had set the limit at 500 ppm; however, the standard was changed back to 1000 ppm with the 1979 edition.

The problem with the USN air purity standard is that the USN has in fact a double standard. USN Standards For Compressed Air 5.3.2 (see Attachment C) state that, "Compressed air must contain adequate oxygen and be free of excessive contamination from carbon monoxide, carbon dioxide, gaseous hydrocarbons, particulates (dirt and dust), oil mist, and other impurities." Section 5.3.2 includes the listing of USN standards, including the 1,000 ppm maximum for CO₂. However, the section immediately following (Other Sources For Air 5.3,3) permits Navy personnel to obtain compressed air in the absence of Navy sources from civilian agencies or firms only if it meets the requirements of Grade A or C air as specified by FED SPEC BB-A-1034A and the diving air purity standards. FE13 SPEC BB-A-1034 as listed in the USN manual (see Table N-1 in Attachment C) differs from the USN standard by requiring CO₂ not to exceed 500 ppm among a whole host of other more stringent requirements. Clearly the US Navy is requiring outside sources for diving compressed air to provide higher quality air than the U.S. Navy requires of its own diving units even when the USN standards are described in Section 5.3.2 as being, "free of excessive contamination."

Since physiological effects of gases are controlled by their partial pressures, any discussion of limits must consider partial pressures while regulations and standards are stated in percentages and/or concentrations in ppm. Therefore it is necessary to consider the impact of carbon dioxide at potential diver depths. The USN frequently evaluates or considers the effects of air on divers at a maximum exposure depth of 10 atmospheres absolute pressure (10 ATA or 297 feet of sea water, fsw). A diver at this depth with a breathing mixture containing 1000 ppm CO₂ would be exposed to a surface equivalent of 10,000 ppm CO₂. This same limit may have been used to derive the CO₂ limit for National Aeronautics and Space Administration (NASA) Space Shuttle operations. NASA's limit is set at 7.6 mm Hg or 1.0% surface equivalent for normal shuttle and extra-vehicular activities (Nicogossion et al., 1994). Shuttle internal pressure is maintained at I ATA. At this pressure and limit, CO₂ is here again permitted to reach a surface equivalent of 10,000 ppm CO₂. Most recently, reported levels of CO₂ in the Mir space station as high as 8.0% and other problems caused NASA director of shuttle-Mir operations, Frank Culbertson, to say he will stop sending astronauts to Mir if it becomes too dangerous.

Diving medical authorities have addressed the level of CO₂ in breathing mixtures for divers. Youngblood and Wolfe (1976, see Attachment G) while discussing a USN limit for saturation diving state, "Since normal men can tolerate with impunity long-term exposure to CO₂ partial pressures of 21 mm Hg, or 3 % surface equivalent, it would seem reasonable to establish more realistic guidelines." Three percent surface equivalent constitutes a level at 30,000 ppm at the surface, a level which is three times the allowable exposure permitted for a space shuttle crew or a USN. diver at 297 fsw. Edmonds et al. (1992, see Attachment H) described a 300 ppm standard for CO₂ as, "too strict because the USN maximum limit of 0.1% would not be toxic to the depth limits of compressed air diving and would be easier for compressor operators to meet." Sinclair et al. 1971 (see Attachment I) note that a healthy man at rest can tolerate an ambient PCO₂ of up to 3G mm Hg (3.9% surface equivalent) without signs or severe symptoms of incapacitating physiological changes.

Actual research studies of the effects of CO₂ levels on humans offer the best rationale for modifying the safety guidelines. The Sinclair et al. (1971) limit for incapacitating physiological change while at rest equates to a limit of 3.95% or 39,500 ppm surface equivalent, a value very close to human expired air. If this were an allowable exposure limit, the equivalent limit for a diver to 297 fsw would be an approximate 3,950 ppm surface value. Youngblood and Wolfe (1976) list the lowest level of adverse effect for acute CO₂ poisoning (increased respiratory stimulation and general arousal) as occurring at concentrations of between 4 and 6 % CO₂ (sea surface equivalent). Over an exposure period of 40 days, no biochemical effects were noted for CO₂ concentrations in air up to 0.5% (5,000 ppm) while adaptive biochemical changes, described as mild physiological strain, occurred between 0.5 and 3 %, NOAA (1991, see Attachment J), Shorter durations permitted higher concentrations. These data indicate there is no justification for picking 500 over 1000 ppm CO₂ as a standard.

The recreational (SCUBA) diving community within the U.S. has a widely stated maximum depth limit of 130 fsw (5 ATA) for air diving. The depth of 130 fsw is also the maximum limit for SCUBA operations in both the OSHA and LSCG Commercial Diving Regulations. Any standard permitting breathing air for SCUBA to contain up to 1000 ppm would potentially expose a diver to a maximum surface equivalent of 0.5% at the maximum depth of 130 fsw, below the level for notable physiological effect as stated above and half that allowed on NASA Shuttle flights.

All entities involved with diving are concerned with diver safety. However, when a more restrictive measure does not indeed improve safety it serves no useful function and in this case causes problems. Average ambient air may range in CO₂ content from 350 ppm (CRC, 1996; see Attachment K) to as high as between 370 and 380 ppm (Edward Galla, Texas Research Institute, Austin, TX, pers. comm.). This is a gas which varies seasonally and which is on the increase (CRC, 1996 and Galla, pers. comm.). With ambient CO₂ approaching 380 ppm the atmosphere is approximately 75% of the way to failure of the Grade E standard.

Lastly I appeal to you to consider the impact of this standard in our present litigation prone society. If there is no physiological basis (therefore safety basis) for a standard set at 500 ppm CO₂ and it is a value which is difficult for many to achieve, think of the legal position in which we may be placed by such a standard.

Thank you for your consideration on this matter. If I may be of any assistance by providing additional information, please do not hesitate to call on me.

Sincerely,

D.E.E.P., Inc.

Larry R. Martin President