Posted by Steve on August 06, 2001 at 20:22:21:
In Reply to: Re: Nitrox question - non O2 cleaned cylinders posted by DMU on August 06, 2001 at 18:31:02:
Good point about the back and forth exchanges without facts. I found this which has some info on regulations however we have MHK who is challenging these rules "myths" whatever.
MYTHS AND MISCONCEPTIONS
OF OXYGEN PERCENTAGES FOR OXYGEN SERVICE
by Dick Rutkowski
The myths and misconceptions of oxygen percentages for oxygen service come from many sources. Many pseudo-experts read about one type of oxygen service and apply that information to other types of oxygen service. When we talk about percentages of oxygen or try to make regulations pertaining to percentages of oxygen we must understand how oxygen reacts under various circumstances… 1. Physiology 2. Flammability and 3. Chemical or spontaneous ignition...
I. Physiology: Man has lived on planet earth for several thousand years and has become acclimated to 21 percent oxygen. For breathing purposes we like to keep the oxygen between 19.5 and 22 percent. OSHA insures that humans get this amount in industry while working in all environments. USN has set breathing air standards for the diving industry, which OSHA accepts. It happens to equal CGA grade 'E" which most dive shops try to comply with by quarterly analysis of their compressor air (CGA has never set diver breathing air standards this was done by USN). Another important reason is that the algorithms of the decompression tables are based on 79 percent inert gas. If the oxygen content is off by more than one percent, the algorithms are off for decompression which may lead to decompression sickness.
2. Flammability: If fire starts in any space. It is best to have the oxygen content of that space as close to 21 percent as possible. When one increases the percentage of oxygen in a compartment by five percent, the flame spread rate goes up by 34 percent. USN Dive Manual states that the P02 in any chamber, diving bell or other living space should never exceed 25 percent. For flammability purposes, it would be best to have the oxygen around 12 percent rather than 21 percent, but definitely not up as high as 40 percent because if a fire did start in any compartment there would not be a chance in hell of a person trapped in that compartment putting out that fire as it would be raging too rapidly.
Note. In the case of flammability something or someone must start the fire. This is not chemical, but mechanical, and not spontaneous ignition.
3. Spontaneous Chemical Ignition: When over 40 percent oxygen comes across a petroleum based hydrocarbon it can and will chemically ignite; no source of ignition is needed As has been proven repeatedly for 50 years, this does not occur until the percentage of oxygen is between approximately 5O and 100 percent. Standards have been set for the diving industry by OSHA, USN, NOAA and the USCG for using all diving equipment as cleaned for divers breathing air for mixtures of gases up to 40 percent oxygen without additional oxygen cleaning or compatibility for oxygen service.
OSHA Code Of Federal Regulations, Part 1910,430(I)
(Commercial Diving Operations)
The standards contain requirements for the safe use of oxygen which apply to all components connected into the oxygen system. Equipment used with pure oxygen or with mixtures containing over 40% oxygen by volume must be properly designed for oxygen service. All components (except umbilicals) used in such service (or with mixtures over 40% oxygen by volume) must be cleaned of flammable materials. before use.
Finally, oxygen systems carrying over 125 pounds per square inch gauge (psig) and compressed air systems carrying over 500 psig must have slow opening shutoff valves in order to prevent the rapid buildup of pressure and temperature in the system. All these requirements are meant to reduce the hazards of ignition and combustion present within oxygen Systems.
NOAA Oxygen Specifications
Appendix "D" NOAA Nitrox I Diving and Decompression Tables. "High pressure storage cylinders, SCUBA tanks, regulators and all high pressure transfer equipment used with pure oxygen or with nitrox mixtures containing more than forty percent oxygen must be cleaned and maintained for oxygen service."
United States Navy Oxygen Specifications
U.S. MlL-STD-777E (SH) Note K-6-4, Cat. k.6
Mixed Gas, 4500 PSI Service, 15OoF Max
For systems with oxygen content greater than 40% by volume oxygen systems components shall be cleaned in accordance with the requirements of MlL.-STD-1330.
United States Coast Guard Oxygen Specifications
Title 46 - Shipping, revised as of October 1, 1992
Chapter I - Coast Guard, Department of Transportation
Subchapter V - Marine Occupational Safety and Health Standards
Part 197 - General Provisions
Subpart B - Commercial Diving Operations
Periodic Tests and Inspection of Diving Equipment
§ 197.452 Oxygen cleaning
46 CPR 197.451
The diving supervisor shall ensure that equipment used with oxygen or oxygen mixtures greater than 40 percent by volume is cleaned of flammable materials -
(a) Before being placed into service; and
(b) After any repair, alteration, modification, or suspected contamination.
For systems with oxygen content greater than 40% by volume, oxygen Systems components shall be cleaned in accordance with the requirements of MIL-STD-1330.
SOURCE: CCD 76-009. 43 FR 53683, Nov.16. 1978
Authority ~ 33 U.S.C. 1509:43 u.s.c 1331:46 U.S.C. 3306,3703 6101:49 CFR 1.46
Hundreds of thousands of scuba tanks, regulators and helmets have been used with Nitrox mixtures up to 40 percent 02 and there has never been a problem with so called "explosion" or with oxygen fires.
One can place a piece of paper in 100 percent oxygen and not have chemical ignition, but one can light paper in. 21 percent oxygen and have a fire. This is the difference between flammability and chemical ignition. Those of us who have been in the professional field of diving will continue to go along with research and the federal regulations for oxygen up to 40 percent and for oxygen service rated equipment for oxygen percentages over 40 percent, as outlined by OSHA, USN, NOAA and USCG, and not by those who wish to profit by using the standard that any equipment that sees more than 23 percent must be O2 service rated. If this is the case then we must oxygen service rate the whole world. Lets get together and use science not BS in this matter.
The International Association of Nitrox and Technical Divers, Inc. (IANTD), is very much concerned with the safe handling and safety for the use of oxygen. IANTD has set forth standards for oxygen service, oxygen cleaning and oxygen compatible systems for all mixtures of oxygen enriched air and trimixtures. IANTD complies with the safety standards of OSHA, USN, NFPA, and NOAA, for Handling oxygen mixtures with less than 40 percent and oxygen mixtures above 40 percent. Regulations regarding oxygen mixtures less than 40 percent are set forth in the USN, NOAA and OSHA Standards for Mixed Gas Diving Operations as above, for chemical ignition, not for flame spread rates...
Dick Rutkowski retired as the Deputy NOAA Diving Coordinator with 35 years of Federal service and is the past director of the NOAA Hyperbaric Facility, founder of Hyperbarics International, inc., IANTD (1985), and co-founder of ANDI (1989).
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