O2 Cleaning: Some Harsh Chemical Realities


Larry "Harris" Taylor, Ph.D.

 This is an electronic reprint of an article that appeared in IANTD Journal, (Feb/Apr. 1994, p. 8-10). This material is copyrighted and all rights retained by the author. This article is made available as a service to the diving community by the author and may be distributed for any non-commercial or Not-For-Profit use.

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There is no question that material used for oxygen service must be oxygen cleaned. (See Compressed Gas Association (CGA) and National Fire Protection Association (NFPA) references, below). The potential for disaster associated with the increased flammability of all materials in an oxygen rich atmosphere necessitates that all potential combustible material be removed. There is a variety of oxygen cleaning protocols that address this necessity. The specific procedure utilized will depend upon the chemical nature of the potential contaminant, the amount of material to be removed, the physical location and composition of the O2 distribution system, the cost of materials and safeguards, and the experience of the technician who does the cleaning. Typical cleaning methods include steam cleaning, vapor degreasing, solvent washing, alkaline (base or caustic) immersion, acid cleaning, mechanical cleaning (wire brushes, etc.) and purging. Many of these procedures pose a significant chemical health hazard. This article reviews these hazards and suggests some safeguards to minimize the risk. 

Steam/Hot Water Cleaning 

Steam cleaning is the most chemically benign procedure. In general, the object to be cleaned is either submerged in a vat of hot water or subjected to a stream of steam. The combination of heat, agitation or pressure of the flowing fluid removes common dirt, oils, greases and soaps, After cleaning, any remaining water soluble detergent is removed with a vigorous warm water rinse and dried under a stream of oil-free air or nitrogen. 

The detergents commonly used in steam cleaning are considered to be mild skin irritants. Precautions during use include protection of the skin, particularly the eyes, by using protective clothing and safety glasses. If mixing of bulk solid detergents is involved, then respiratory filters should be worn to avoid inhaling the powder. If skin is contaminated, the detergent can generally be removed with a cool water rinse. The most likely injury is thermal burns caused by handling warm or hot material. Wearing appropriate garments and handling the cleaned components with safety tongs best prevent skin contamination and injury. 

Caustic Cleaning 

Caustic agents (chemical bases such as sodium or potassium hydroxide) are used to remove heavy or stubborn surface contamination. The cleaning chemicals are removed with multiple, vigorous water rinses. Strong bases will rapidly attack and degrade aluminum and aluminum alloys. These agents are extremely destructive to body tissues and may cause severe chemical burns. Inhalation can be fatal. 

Prevention of injury involves working in well-ventilated areas, using approved containers, wearing safety glasses, protective clothing and rubber gloves. In case of skin or eye contact, wash affected area with running water for a minimum of 15 minutes. If the eyes are involved, hold the eyelids open to insure adequate irrigation. The eyes are particularly vulnerable to injury by chemical bases; eye contact should be considered a medial emergency. If inhaled, remove victim to fresh air, give artificial respiration, if needed. (If breathing is labored, supplement breathing with oxygen). Seek immediate emergency medical care. 

Acid Cleaning 

Acids are used to remove oxides, light rust, and light oils. Phosphoric acid can be used for all metals. Hydrochloric acid is generally reserved for carbon and low alloy steels. It should not be used with stainless steel. Chromic acid and or nitric acid based agents are recommended for aluminum, copper, and their alloys. Acid cleaning techniques should not be used unless the manufacturer of device being cleaned has specified this procedure be employed. Following their use, acids are removed by rinsing with copious amounts of clean, running water. This rinse is critical! Diver injury has resulted from inhaling residual hydrochloric acid fumes in a "cleaned" scuba cylinder. 

Concentrated acids may be lethal, if inhaled or swallowed. However, the most common injury is tissue destruction (chemical burns) of mucous membranes in the upper respiratory tract, eyes and skin. The best prevention is mechanical isolation: work in a well-ventilated space, use only materials that are acid compatible, wear safety glasses, rubber gloves, and protective clothing. In case of contact, wash the affected area at least 15 minutes with copious amounts of cool running water. If the eyes are involved, separate the eyelids to insure adequate flushing. If the acid has been inhaled, move to fresh air; provide artificial ventilation (if needed; oxygen supplemented if breathing is labored). Seek immediate medical attention. Wash contaminated clothing before reuse and discard contaminated foot ware. 

OXIDIZING AGENTS: Chromic acid is commonly found in glass cleaning solutions. As such, it should be stored separate from any organic solvents or acids. (For example, chromic and acetic acid stored together is a common explosive hazard found chemical storage areas.) Use only as specified by manufacturer or vendor of the process utilized in cleaning procedures. Along this same line, a number of years ago, a very gifted chemistry student, faced with cleaning a rather nasty, solid mass in some lab glassware, figured that if a mixture of chromic acid and sulfuric acid (common commercial glass cleaning solution), a better cleaner could be obtained by mixing potassium permanganate (a strong oxidizer) and sulfuric acid. While this is theoretically solid thinking, the problem is that potassium permanganate and sulfuric acid give rise to a highly explosive and easily detonated mixture. An appearance of a rapidly expanding purple gas cloud is often the last thing seen when this mixture is made. In this particular incident, the student survived the explosion. Left a trail of bloody palm prints along the lab wall as, blinded, he felt his way to the safety shower. He walked away, but with permanent disfigurement from the combination of glass lacerations and acid burns. The point of this little story is that mixing cleaning agents is NOT a good idea AND that in chemistry (as in diving and all life activities), it is often that which is unknown that poses the greatest risk. 

ORGANIC SOLVENTS:  Organic solvents such as carbon tetrachloride, chloroform, methylene chloride (dichloromethane), refrigerant 11 (trichlorofluoromethane), refrigerant 113 (trichlorotrifluoethane), perchloroethylene, 1,1,1-trichloroethane (methylchloroform) or trichloroethylene are often employed in industry as degreasers. These reagents commonly also contain corrosive inhibitors and/or chemical stabilizers to prevent decomposition of the chlorinated chemicals. 

These are powerful solvents. They will dissolve most greases and oils. This is why they have been employed in the dry cleaning operations. In addition they will dissolve or leach material from many common plastics. Users of these solvents need to check compatibility of containers and object being cleaned with these materials. 

These solvents are harmful if swallowed, inhaled or absorbed through the skin. Their vapors are irritating, especially to the eyes and mucous membranes of the upper respiratory tract. Direct skin contact is quite destructive to tissue. Carbon tetrachloride and trichlorethylene are particularly toxic. Inhaling the common solvent 1,1,1-trichloroethane can lead to distorted perceptions of reality, hallucinations, behavioral instability, diarrhea and headache. Consumption of alcohol may increase the toxic effects of this class of solvents. 

All chlorinated solvents pose a health risk to humans. Once absorbed or inhaled, they will accumulate in the liver and kidneys. Often, there are central nervous system and cardiovascular impairment side effects. Eventually, enough material will accumulate and organs will cease to function. (As a practicing organic chemist, my rule of thumb is "If I can smell it, the chemical is going to my liver (body's primary detoxification center), but if it has a chloro in the name, it may never leave my body.")   Some of these compounds (dichloromethane, in particular) will decompose in the body to form carbon monoxide. Many of the chlorinated hydrocarbon solvents have been demonstrated to be carcinogenic. Those not formally labeled carcinogenic are generally believed to be so. Most, particularly 1,1,1-trichloroethane have been demonstrated to be mutagenic. If spilled on leather shoes, the trapped solvent can create blisters and other skin lesions on the foot. 

Many of these chlorinated solvents have been used in fire extinguishing agents. However, when heated, these materials can decompose to such nasty compounds as carbon monoxide, hydrochloric acid, hydrofluoric acid, and phosgene (a very powerful chemical warfare agent used for its ability to attack lung tissue). Since these life threatening products of decomposition can also be formed in many common chemical reactions, chlorinated solvents should not be stored near heat sources, strong oxidizing agents, strong acids, strong bases, or near aluminum, magnesium, potassium, or sodium metals. Some of these chlorinated solvents are flammable when combined with an oxidizer, so it is critical that all such solvents be entirely removed before exposure to oxygen enriched atmospheres. There have been spectacular explosions resulting from the ignition of chlorinated solvents in oxygen systems! 

Aluminum is a porous metal. Thus, use of chlorinated solvents in cleaning aluminum scuba cylinders will result in some solvent being absorbed into the walls of the cylinder. Toxic chlorinated solvent and by products will then be slowly released into the gas contained within the cylinder. I am aware of no data that examines this risk to the diver if such solvents are used for scuba cylinders, but I would NOT want to be part of the alpha test group. In addition, many of these solvents slowly form hydrochloric acid that is known to attack and degrade aluminum metal. If using chlorinated solvents, it is wise to check with the cylinder or regulator manufacturer to check for compatibility. 

If chlorinated solvents must be used, then several safeguards should be employed to insure the health and safety of those exposed. Such solvents should only be used in well-ventilated areas. The user should be protected with adequate clothing, eyeglasses and gloves. Since these solvents dissolve or pass through most common glove materials, the preferred material for gloves is Viton. (These gloves are very expensive, but much cheaper than a liver transplant!) 

In case of skin contact, flush exposed area with copious amounts of water for a minimum of 15 minutes. Assure adequate flushing of the eye by manually holding the eyelids open. If the solvent has been inhaled, move to fresh air; provide artificial ventilation (if needed: oxygen supplemented if breathing is labored). Seek immediate medical attention. If swallowed, rinse mouth with water (if victim is conscious) and seek immediate medical attention. 

The used solvent also poses a health hazard. These materials are water insoluble and should not be poured down the drain. Proper disposal usually involves a commercial vendor who specialized in handling waste materials. Most often these solvents are re-distilled for recycling, but total destruction typically involves extreme high temperature ignition. 

Since these materials are commonly listed by a variety of environmental protection enforcement agencies as hazardous, they are subject to a number of regulations and disposal procedures.  Violation of these laws can be extremely damaging to the environment and most expensive for the offender. Those using these materials should consult local and regional authorities for guidelines. 

Inspection Hazards 

One method of inspecting the cleaned component for residual contamination is observation of the part under ultraviolet ("black" or UV) light. This method only works for materials that fluoresce (emit light when excited by UV light). Many contaminants and most residual solvents will NOT fluoresce. So, inspection under UV light should not be the sole criteria for acceptance of O2 clean status. Users of UV light should be aware that this light could damage the skin (sunburn is a result of ultraviolet light from the sun) and the eyes. Even if not looking directly into the light source, reflected UV light can cause permanent damage to the eyes by burning the retina. Whenever the UV inspection light is used, the inspector should be wearing glasses specifically designed to stop UV radiation. Users should not look directly into the light source. 

The OSHA Specter 

In 1971 the Occupational Safety and Health Act (OSHA) became law. This act is without a doubt the most comprehensive health and safety legislation in the history of the world. This act mandates that EVERY employer in the United States provide a working environment that is "free" from recognized hazards. This set of regulations has teeth: employers found in violation of OSHA standards are subject to extensive fines (may be assessed daily until compliance is documented) and imprisonment. In November of 1983, the Hazard Communication Standard (HCS) extended the chemical regulations, which had been aimed primarily at the chemical manufacturing industry. This is a generic document that regulates ALL hazardous chemicals used by ANY employer in the United States. This law, commonly referred to as "Right To Know" mandates the following: 

1. Chemical manufacturers must evaluate the hazards of all chemical products they produce. 

2. Users of chemicals MUST provide their employees with information on chemical hazards using a formal chemical hazard communication program. (Many have adopted a so-called "Chemical Hygiene Program.") 

3. This hazard communication program must include hazardous labels, Material Safety Data Sheets (MSDS), warning signs and employee training. 

Unless state laws are more stringent, the federal Right To Know legislation applies to ALL users of chemicals in the United States. With time, OSHA will be "visiting" all users of chemicals to insure compliance with federal OSHA chemical safety standards. 

Translation: For compliance with federal OSHA regulations, every employer must make available to his employees: a set of written instructions which identify hazardous materials, the manufacturing safety data sheets for all chemicals used on the premises, warning labels on containers, safety warning signs in areas where hazardous materials are used and proper training in the safe handling of hazardous materials. Finally, the employer must be able to document compliance to OSHA. 

Beyond OSHA 

In addition, users of hazardous chemicals must make certain that their method of disposal of harsh chemical materials is appropriate. Remember, hazardous waste poured down the drain or allowed to evaporate into the air will eventually contaminate the water in which you or your children will dive. The Environmental Protection Agency (EPA) may regulate by local ordinance or guidelines the safe disposal of chemical waste (which may include removal by a commercial vendor). 

Those filling oxygen cylinders should be aware that there are numerous regulations concerning the transfilling of oxygen cylinders used for human respiration. It is possible the Federal Drug Administration (FDA) could consider oxygen cylinders used for decompression to be regulated by their Compressed Medical Gases Guidelines. This may include licensing of the transfilling station. Lastly, those filling oxygen cylinders should be aware that several oxygen cylinders used in-water have violently ruptured during filling. As a result, the CGA has specifically recommended that oxygen cylinders NOT BE USED UNDERWATER. 


The extreme risk of fire and explosion associated with oxygen enriched atmospheres mandates oxygen cleaning. The cleaning process, however, has its own set of risks: handling and disposing of hazardous chemicals. Understanding the nature of the problem, as with all risks in diving, can minimize these risks. Wise people providing oxygen-cleaning services will consult chemical hygiene and legal authorities to minimize all risks associated with the process. 

References: Chemical Hazards 

Fawcett, H. & Wood, W. SAFETY AND ACCIDENT PREVENTION IN CHEMICAL OPERATIONS, Wiley-Interscience, New York, NY. 1982. 

Green, M. & Amos, T. SAFETY IN WORKING WITH CHEMICALS, Mac Millian Publishing, New York, NY. 1979. 

Manufacturing Chemists Association, GUIDE FOR SAFETY IN THE CHEMICAL LABORATORY, Van Nostrand Reinhold, New York, NY. 1970. 


Steere, N. THE HANDBOOK OF LABORATORY SAFETY, Chemical Rubber Co. Cleveland, OH. 1971. 

References: CGA Publications 

CGA G-4: Oxygen. 

CGA G-4.1: Cleaning Equipment For Oxygen Service. 

CGA G-4.3: Commodity Specification For Oxygen. 

CGA G-4.4: Industrial Practices For Gaseous Oxygen Transmission And Distribution Piping Systems. 

CGA G-4.6: Oxygen Compressor Installation And Operation Guide. 

CGA. P-2.5: Transfilling Of High Pressure Gaseous Oxygen To Be Used For Respiration. 

CGA P-14: Accident Prevention In Oxygen-Rich And Oxygen Deficient Atmospheres. 

CGA SB-7: Rupture Of Oxygen Cylinders In The Diving Industry. 


References: FDA 

Compressed Medical Gases Guideline 

References: NPFA Publications 

NFPA 43C: Storage Of Gaseous Oxidizing Materials. 

NFPA 50: Bulk Oxygen Systems At Consumer Sites. 

NFPA 53M: Fire Hazards In Oxygen-Enriched Atmospheres. 

NFPA 69: Explosion Prevention Systems. 

NFPA 99B: Hyperbaric Facilities 

LC-HAZ-91: Fire Protection Guide To Hazardous Materials 

References: OSHA 


Moran, R. HOW TO AVOID OSHA, Gulf Publishing Co. Houston, TX. 1981. 

Petersen, D. THE OSHA COMPLIANCE MANUAL, McGraw Hill, New York, NY. 1975. 

Ruch, W. RESPIRATORY PROTECTION: OSHA AND THE SMALL BUSINESSMAN, Ann Arbor Science Publishers, Ann Arbor, MI. 1975. 

Showalter, D. HOW TO MAKE THE OSHA-1970 WORK FOR YOU, Ann Arbor Science, Ann Arbor, MI. 1976. 

Wagner, T. COMPLETE GUIDE TO HAZARDOUS WASTE REGULATION, Van Nostrand Reinhold, New York, NY. 1991. 

Young, J. Kingsley, W. & Wahl, G. DEVELOPING A CHEMICAL HYGIENE PLAN, American Chemical Society, Washington, D.C. 1990. 


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About The Author: 

Larry "Harris" Taylor, Ph.D. is a biochemist and Diving Safety Coordinator at the University of Michigan. He has authored more than 100 scuba related articles. His personal dive library (See Alert Diver, Mar/Apr, 1997, p. 54) is considered one of the best recreational sources of information In North America.

  Copyright 2001-2022 by Larry "Harris" Taylor

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