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 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
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 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.
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
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.
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
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
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
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
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
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
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.
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
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
3. This hazard communication program must include hazardous
labels, Material Safety Data Sheets (MSDS), warning signs and employee
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.
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.
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.
Sax, N.C DANGEROUS PROPERTIES OF INDUSTRIAL MATERIALS, Van
Nostrand, New York, NY. 1979.
Steere, N. THE HANDBOOK OF LABORATORY SAFETY, Chemical Rubber Co. Cleveland, OH. 1971.
CGA G-4: Oxygen.
CGA G-4.1: Cleaning Equipment For Oxygen
CGA G-4.3: Commodity Specification For
CGA G-4.4: Industrial Practices For Gaseous Oxygen
Transmission And Distribution Piping Systems.
CGA G-4.6: Oxygen Compressor Installation And Operation
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
CGA SB-7: Rupture Of Oxygen Cylinders In The Diving
HANDBOOK OF COMPRESSED GASES
Compressed Medical Gases Guideline
NFPA 43C: Storage Of Gaseous Oxidizing
NFPA 50: Bulk Oxygen Systems At Consumer
NFPA 53M: Fire Hazards In Oxygen-Enriched
Explosion Prevention Systems.
Explosion Prevention Systems.
NFPA 99B: Hyperbaric Facilities
LC-HAZ-91: Fire Protection Guide To Hazardous Materials
Lowry, G. LOWRY'S HANDBOOK OF RIGHT TO KNOW AND EMERGENCY
PLANNING, Lewis Publishing, Chelsea, MI. 1988.
Moran, R. HOW TO AVOID OSHA, Gulf Publishing Co. Houston, TX.
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.
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.
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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.
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These articles may be used for not-for-profit diving education