Safety In Underwater Cutting And Welding


This appendix is intended to cover safety precautions to be followed while preparing for and conducting underwater cutting or welding operations. All personnel should read and comprehend the safety precautions listed in this section and the safety summary contained in the front section of this manual. Deviation from established standards are of course potentially dangerous; however, the most serious aspect of disregarding safety rules may not be the initial deviation, but the tendency to treat other rules just as casually. Remember, safety is a full-time job and the more safety-conscious each team member becomes, the safer each diving operation becomes.

For detailed information on chemical hazards encountered in salvage, refer to the U.S. Navy Ship Salvage Safety Manual, (S0400-AA-SAF-010), which covers toxic, explosive, corrosive and other special nature perils.


Underwater cutting and welding operations involve several hazards, including lethal electrical currents, oxygen and hydrogen rich gases which will explode in the presence of a spark and electrode tip temperatures in excess of 10,000°F. It is impossible to anticipate all possible situations that may arise in underwater cutting or welding operations. Consequently, it can not be assumed that safe operating conditions will exist simply by blindly following the guidelines set forth in this manual. Nonetheless, with a thorough knowledge of cutting and welding fundamentals combined with the use of common sense and sound judgment, the procedures described in this manual can be performed in maximum safety.


Do NOT attempt to speed up the cutting by creating a fire or inferno deep inside the metal. Such a situation can lead to an explosion.



A diver is at risk to severe electrical shock when performing a cutting or welding operation while only partially immersed in water. Hence, the splash zone is the most hazardous location in which a diver can be placed.


NEVER bring a cutting torch into a bell with the oxygen on or with the welding generator running.

D-3.1 General Information. Gases produced by underwater cutting are rich in oxygen and hydrogen and will explode if trapped and ignited. Gases from underwater cutting will collect in closed compartments, open tubular structural members, open piping systems, shaped structural members and under such members as "H" beams. Before cutting, it is mandatory that provision be made to evacuate existing gases and eliminate the possibility of further gas entrapment. Refer to Naval Ships Technical Manual NAVSEA S9086-CH-STM-030/CH-074 Volume 3 for detailed information on gas-free engineering.

If the presence of trapped explosive gas mixtures is uncertain, it may be necessary to drill holes in suitable locations to allow the gases to escape. This will flood the compartment with sea water. An alternative would be to purge the compartment with a mixture of gases which will not support combustion.

D-3.2 Specific Information. Underwater cutting and welding processes generate explosive gases.

• When cutting with power on or welding, hydrogen and oxygen are dissociated from the water and will travel separately as bubbles. These bubbles can collect in a trapped or confined space overhead. As the hydrogen and oxygen gases combine they will ignite, causing a popping sound.

• Oxygen cutting is about 60 percent efficient, resulting in approximately 40 percent pure oxygen being released into the environment. This gas can become entrapped above the work area, and when combined with a fuel such as hydrocarbons, can easily be ignited by a hydrogen bubble or a spark trapped in the bubble.

Any pop is a sign of explosive gases collecting above the underwater work area and is the point when cutting or welding must stop and the cause investigated.

Prior to the start of any underwater cutting or welding, as built drawings and physical configuration of the work area must be studied to determine all these areas and voids that could contain or trap explosive gases. These areas and voids must be vented or made inert in accordance with Naval Ships Technical Manual NAVSEA 59086-CH-STM-030/CH-074 Vol 3 to prevent possible explosions.

Care should also be taken when cutting or welding on enclosures that are on or above river beds, especially in mud, because trapped methane gas in the proper concentrations can explode.

Explosive gases may be produced by any one or a combination of the following:

• Petroleum products such as gasoline, fuel oil or greases;

• Paint mixing mediums, such as linseed oil or thinners;

• Epoxies, adhesives and solvents;

• Ammunition or bulk explosives;

• Decaying vegetable or animal matter; and

• Unburned gases from cutting torches.

Every precaution must be taken to prevent an underwater explosion. To minimize the possibility of explosions from trapped gasses, the following procedures are recommended:

a. Start cutting at the highest point and work downward.

b. When cutting thick material, i.e., propeller shafting, cut from the outside and work around the circumference. By withdrawing the electrode every few seconds to allow water to enter the cut, exceedingly high temperatures can not build up inside the metal. A brushing or stroking action in the direction of the intended cut should be used.

c. Gases may be vented to the surface with a vent tube (flexible hose) secured in place from the high point where gases would collect to a position above the waterline.

d. When working under a sea chest, gas can be vented by briefly opening an internal valve or by the above method.



AC power shall not be used for underwater cutting or welding due to the extreme danger involved with AC current underwater. Electrical shock produced by AC current prevents voluntary relaxation of the muscles controlling the hand. Consequently, the diver may be unable to let go if his body or equipment accidentally enters the electrical circuit.

Electricity and water are incompatible by nature and the use of electrically powered equipment underwater presents a potential shock danger to both the diver and the tender. When using electrically powered equipment such as cutting, welding or underwater lighting, the diver and tender must be protected from electric shock. All personnel engaged in underwater cutting and welding should be thoroughly trained in CPR and first-aid so they can render immediate assistance in the event of an accident.

The results of a study conducted for the Navy revealed that the principal underwater electrical hazard facing divers engaged in welding and cutting is non-lethal electric shock. The hazard exists when a diver wearing inadequate protective dress is in close proximity to a relatively high-powered source of electricity. AC power was found to pose a considerably greater threat to the diver than DC, therefore AC power will NOT be used for underwater cutting or welding.

Electrical current above shock levels that passes through human tissue is known to temporarily alter the physiological function of cells. The long-term effects, if any, are unknown. Much greater levels can cause thermal burns. Severe shocks could conceivably result in respiratory or cardiac arrest in divers. In addition, minor shocks may cause loss of control, panic or injury due to involuntary muscle contraction. Therefore, with the exception of a tingle at arc initiation, unpleasant electric shocks should not be tolerated in underwater operations, even though no physiological damage may be immediately apparent.

The safety rules listed in the following sections must be followed to provide maximum personal safety for the diver.


There are many conditions which contribute to making underwater work difficult. These include adverse currents, unstable footing, poor visibility and low temperatures. A constant source of danger comes from the falling or rolling of cut-away pieces. This is especially true in salvage wrecking. These, combined with the dangers involved in operating an electric arc capable of producing fatal shock, severe burns and explosive gas pockets, create a situation where the diver must be extremely alert.

The following precautions must be observed:

a. Careful examination should be made before starting the cut to learn how the cut-away pieces will fall and whether there are any projections, wires or other objects which may foul lines or cause a piece to swing around in an unexpected manner.

b. Be extremely careful when cutting tightly-bound wire rope e.g., wire wrapped in a ship's propeller. When severed, the wire can back-lash with spring-like force.

c. Before cutting, ensure that umbilical and diving equipment will not be in the path of slag from the cutting operation.

d. Avoid cutting overhead if possible, since the falling molten material will seriously damage the diving helmet, dress and umbilical.

e. Never put down or carry an electrode holder while the power is on.

f. Never change an electrode while the power is on.

g. The diver must never allow any body part or equipment to come in contact with the grounded work when the safety switch is closed.

h. Care should be taken with diver-carried large loose metallic items (i.e., wrenches and backpacks) to ensure no contact is made with a live electrode or the work.

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