FIRE AND EXPLOSION PREVENTION DURING WELDING

INTRODUCTION

Welding, cutting, and allied processes produce molten metal, sparks, slag, and hot work surfaces. These can cause fire or explosion if precautionary measures are not followed.

NATURE OF THE HAZARD

Flying sparks are the main cause of fires and explosions in welding and cutting.

Sparks can travel up to 35 feet (10.7 meters) from the work area.  Sparks and molten metal can travel greater distances when falling.  Sparks can pass through or become lodged in cracks, clothing, pipe holes, and other small openings in floors, walls, or partitions.

Typical combustible materials inside buildings include: wood, paper, rags, clothing, plastics, chemicals, flammable liquids and gases, and dusts.   Parts of buildings such as floors, partitions, and roofs may also be combustible.

Typical combustible materials outside buildings include dry leaves, grass, and brush.

Welding and cutting can cause explosions in spaces containing flammable gases, vapors, liquids, or dusts.  Special precautions are needed for any work on containers (see American Welding Society AWS F4.1).

HOW TO AVOID THE HAZARD

·         Develop adequate procedures, and use proper equipment to do the job safely.

·         When Required obtain a Hot-Work Permit (See NFPA 51B).

·         Remove combustible materials for a minimum radius of 35 feet (10.7 meters) around the work area or move the work to a location well away from combustible materials.

·         If relocation is not possible, protect combustibles with covers made of fire- resistant material.

·         If possible, enclose the work area with portable, fire-resistant screens.

·         Cover or block all openings, such as doorways, windows, cracks, or other openings with fire resistant material.

·         Do not weld on or cut material having a combustible coating or internal structure, such as in walls or ceilings, without an appropriate method for eliminating the hazard.

·         When needed, have a qualified firewatcher in the work area during and for at least 30 minutes after the job is finished.

·         After welding or cutting, make a thorough examination of the area for evidence of fire. Remember that easily visible smoke or flame may not be present for some time after the fire has started.

·         Do not dispose of hot slag in containers holding combustible material.

·         Keep appropriate fire extinguishing equipment nearby, and know how to use it.

·         Make sure all electrical equipment and wiring are installed properly and have recommended circuit protection.

·         Do not overload or improperly size input conductors and/or weld output conductors to avoid equipment and building fire hazards.

·         Connect the work cable to the work as close to the welding area as practical.

·         Do not weld or cut in atmospheres containing reactive, toxic, or flammable gases, vapors, liquids, or dust.

·         Do not apply heat to a workpiece covered by an unknown substance or coating that can produce flammable, toxic, or reactive vapors when heated.

·         Do not apply heat to a container that has held an unknown substance or a combustible material unless container is made or declared safe.  (see AWS F4.1).

·         Provide adequate ventilation in work areas to prevent accumulation of flammable gases, vapors, or dusts.

SUMMARY

Remember that sparks can travel up to a radius of 35 feet (10.7 meters) from the work and pass through or become lodged in all kinds of openings and cause fires where least expected.   Recognize that sparks can travel well beyond the 35 foot (10.7 meters) radius when falling or during plasma arc cutting and air carbon arc cutting or gouging. Remove combustible materials and prevent flammable gases, vapors, and dusts from accumulating in the work area to reduce the possibility of a fire or explosion. Always have appropriate fire extinguishing equipment nearby, and know how to use it.

Fires and explosions can be prevented by being aware of your surroundings, minimizing the combustibles in them, and taking the appropriate protective precautions.

INFORMATION SOURCES

American National Standards Institute (ANSI). Safety in Welding, Cutting, and Allied Processes, Z49.1, available from American Welding Society, 550 N.W. LeJeune Road, Miami, FL 33126.  Phone 800-443-9353; Web site: www.aws.org.

National Fire Protection Association (NFPA), Standard for Fire Prevention During Welding, Cutting, and Other Hot Work, NFPA 51B, available from the National Fire Protection Association,    1 Batterymarch Park, P.O. Box 9101, Quincy, Massachusetts USA 02269-9101.  Phone: 617-770-3000; Web site: www.nfpa.org.

Occupational Safety and Health Administration (OSHA). Code of Federal Regulations,Title 29 Labor, Chapter XVII, Parts 1901.1 to 1910.1450, available from Superintendent of Documents, U.S. Government Printing Office, P.O. Box 371954, Pittsburgh, PA 15250-7954. Phone: 866-512-1800;  Web site: www.osha.gov.

American Welding Society (AWS).  Safe Practices for the Preparation for Welding and Cutting of Containers or Piping, AWS F4.1, available from the American Welding Society, 550 N.W. LeJeune Road, Miami, FL 33126. Phone: 800-443-9353; Web site: www.aws.org.

American Welding Society (AWS).  Fire Safety in Welding and Cutting, Pamphlet, available from the American Welding Society, 550 N.W. LeJeune Road, Miami, FL 33126.  Phone: 800-443-9353; Web site: www.aws.org.

Mine Safety and Health Administration (MSHA). Code of Federal Regulations, Title 30 Mineral Resources, Parts 1-199, available from Superintendent of Documents, U.S. Government Printing Office, P.O. Box 371954, Pittsburgh, PA 15250-7954. Phone: 866-512-1800; Web site: www.msha.gov.

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TO: Director, National Institute for Occupational Safety and Health

FROM: Iowa FACE Program Date of Report: April 6, 1999

SUBJECT: Arc welder dies in explosion while using an old barrel as a worktable.

SUMMARY

A 38-year-old male arc welder died as a result of an explosion at a construction company. The victim was working at a rural shop location to repair a large garbage truck, which was brought to the shop for repairs that morning. Several items were to be added to the rear of the truck and on the main box. The victim was working near a farm building, a 2-story large wood frame structure, which was used as a workshop and for storage of material used in connection with the construction business.

The victim was arc welding some brackets on the back of the truck. He was apparently welding with a wire welder and used a metal 55-gal barrel as a worktable while welding. Apparently the heat or sparks from the welding ignited residual vapors and/or material in the barrel, causing it to explode. The explosion knocked the victim down, and started a fire in the immediate area. An employee heard the first explosion and saw the building on fire near the back of the garbage truck. The employee ran to the area and found the victim, a large/obese man, lying on the ground, with exploded portions of the drum falling about him. The victim was unconscious, and not breathing. When the employee attempted to move the victim, there were secondary multiple explosions and fires, which forced him to stop. The fire increased rapidly and involved propane and acetylene tanks in the establishment. The employee ran and called the local fire department and county sheriff for assistance.
When the fire department and county sheriff arrived on the scene, the entire building was in flames. The fire was extinguished and the victim's body was found near the garbage truck parked to the side of the building. The body was taken to a local hospital for an autopsy.

RECOMMENDATIONS based on our investigation are as follows:

1. Ensure that welders are suitably trained in the safe operation of their equipment and process.
2. Ensure that welding should not be performed on or near used drums, until they have been thoroughly cleaned.
3. Develop, implement, and enforce a written safety program. The safety program should include task specific safety procedures and employee training in hazard identification, avoidance, and control.
4. Designate a competent person to conduct frequent and regular site safety inspections.

INTRODUCTION

At 10:35 AM on May 21, 1998, a 38-year-old male died as a result of an explosion, which occurred while he was welding parts on a garbage truck. The Iowa FACE program became aware of the fatality on May 22, 1998 from a newspaper article. Information was gathered from the county sheriff, fire department, and medical examiner's report. Photographs taken by the state fire marshal’s office were reviewed.


The construction company was owned and operated by the victim's brother, who was also living on the property where the incident took place. However, there was no indication that the victim was working for his brother at the time of the incident. He was working for the garbage truck owner as a freelance welder, repairing and modifying his trucks.


The farm building contained typical electric and water utilities, but they were not involved in the fire. Other environmental conditions were not a contributing factor in this incident.


INVESTIGATION


The victim was at the location to repair a large garbage truck, which was brought to the shop for repairs at 7:00 am. Several items were to be added to the rear of the truck and another item needed to be welded on the main box. There were two heavy pieces of steel that needed to be welded together and then attached to the truck. The base piece was approximately 6 inches by 6 inches and then a second piece was attached to the top. The garbage truck was backed up to the building near a large overhead door on the east side of the building. Another employee noticed the victim welding, with a 'stinger' in his hand just minutes before the explosion. The employee also noticed a large 55-gal drum at the rear of the truck, which was being used by the victim when he was welding.




An employee heard the first explosion and saw the building on fire near the back of the garbage truck and the overhead door. The employee ran to the area at the rear of the truck and attempted to move the victim, but was unable to. He then ran and called for help. 

The local fire department received the call at 10:35 am with a reported fire and explosion. When the fire department and county sheriff arrived on the scene, the entire building was in flames. As they began to control the blaze, they were told that one person was still in or near the structure. A short time later the victim's body was located near a garbage truck parked on the side of the building. The victim was found at the rear of the truck laying face up on the ground. The body had sustained major damage as a result of the fire. 

The victim was removed and taken to the hospital and an autopsy was performed. Autopsy revealed that the victim died from a severe blow to the head and was not killed by the fire. The top of the drum had the impression of the steel piece that was being made for the back of the truck. There were two heavy pieces of steel welded together. A small section of the welding wire was attached to the item. 

Apparently, the victim was working on this at the time. There were also some areas on the drum where hot metal from the welding process had attached to the top of the drum in the location where the impression was found.

The steel item had not been added to the rear of the truck prior to the fire. The top section of the 55-gallon drum was found in the fire debris. The bottom of the barrel was found at the rear of the truck near the victim's body. A heavy steel plate item that was to be added to the rear of the truck was found lying near the drum bottom. According to the State Fire Marshal's report, it appeared that the drum exploded and the bottom stayed in the location where the drum had been.


The State Fire Marshal concluded that the explosion took place when the victim was welding two sections of heavy steel together on top of the 55-gallon drum. The victim had apparently attached the ground lead from the welder to the barrel, which may have caused the barrel to heat up during welding, to the point of igniting the flammable material inside. Another more likely scenario is that the welder simply burned through the lid of the barrel with his welding rod, and directly ignited vapors inside the barrel.


Samples of the interior of the drum were taken for analysis, but the State Fire Marshal's Office was unable to determine what product was in the 55-gallon drum.


CAUSE OF DEATH


The medical examiner’s report stated the probable cause of death as severe traumatic head injuries.


RECOMMENDATIONS / DISCUSSION


Recommendation #1: Employers should ensure that welders are suitably trained in the safe operation of their equipment and process.


Discussion: Fire and explosion may be a risk when welding improperly. Welding should be conducted following the requirements found in 29 CFR Part 1910 and 1926. These regulations specify that employers must insist that welders and their supervisors are suitably trained in the safe operation of their equipment and process. The employer should ensure that suitable fire extinguishing equipment is accessible.


Welding sparks may travel up to 35 feet. To minimize the danger, all combustibles must be moved at least 35 feet from the work site. Combustible items that can't be moved, should be covered with a fireproof blanket. The supervisor should determine the combustible materials and hazards present or likely to be present in the work location.


Arc welding equipment should conform to the design and installation criteria (29 CFR Part 1910 and 1926). Grounding of the welding machine should be checked before welding is started. Coiled welding cable must be spread out. A separate electrical connection should be used to ground the item that is being welded, and the ground lead must be firmly attached to the work.


Recommendation #2: Employers should ensure that welding should not be performed on used drums, until they have been thoroughly cleaned.


Discussion: Welding and other hot work should not be performed on used drums, barrels or other containers prohibited until they have been cleaned thoroughly (29 CFR Part 1910 and 1926). Cleaning should be done to be certain that there are no flammable materials present or any substance such as greases, tars, acids, or other materials which when subjected to heat might produce a flammable or toxic vapor. In this case the victim used an old barrel as a worktable, in retrospect, not a wise idea when arc welding. Even a very small amount of residual fuel, oil, or gasoline vapor, when mixed with appropriate air, became an deadly mixture inside the barrel.


Recommendation #3: Employers should develop, implement, and enforce a written safety program. The safety program should include task specific safety procedures and employee training in hazard identification, avoidance, and control.


Discussion: The implementation and enforcement of a comprehensive safety program is designed to prevent worker injury. The safety program should include task-specific safety procedures and employee training. Training is a critical element in a safety program and in this case, training should include the communication of task-specific safety procedures. All contractors should be advised about flammable materials or hazardous conditions on site.


Recommendation #4: Employers should designate a competent person to conduct frequent and regular site safety inspections.


Discussion: Regular inspections of the work site by a competent person, ensure that safety procedures are being followed, and demonstrate that the employer is committed to the safety program and prevention of injuries. In this case, scheduled and unscheduled inspections should be conducted, and include a review of the jobsite, materials, and equipment to identify hazard conditions.

REFERENCES:
National Safety Council. Accident Prevention Manual for Business & Industry: Administration and Programs. Tenth Edition. Chicago, IL. 1992.

Office of the Federal Register: Code of Federal Regulations, Labor 29 Part 1910 and Part 1926. Washington, DC: U.S. Government Printing Office, 1996.

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SAFE WELDING PRACTICES ON CARGO VESSELS

On a cargo vessel, fire occurred in the mast house where oxygen and acetylene cylinders were stored. The crew had arranged two gas torches in tandem for carrying out hot work on the windlass drum. Both the torches were connected in parallel from the same pair of gas cylinders by temporarily fitting “standard” t-joints at the regulator valves. At sometime during the hot work, it was decided to use one gas torch to carryout brazing repair work on the other torch while it was connected to the pressurized gas hoses.



Flashback from the torch being heated travelled through the hoses up to the mast house, rupturing the hoses at the regulator valve connections and causing a fire inside. Fortunately, the backfire arrestors on the regulators prevented a major explosion of the cylinders.

Such hazardous accidents can take place on any kind of ship if proper precautions are not taken while handling gas welding/cutting on board ships.
Compressed gas cylinders are used in ship’s engine room and deck for a variety of repair and manufacturing operations. The two most used types of gas cylinders for this purpose are oxygen and acetylene.

When performing gas welding or cutting operation, following practical tips must be considered for safety and efficiency of operations and to avoid accidents while carrying out deck operations :

1. Secure in Vertical Position: Compressed gas cylinders must be handled with utmost care and always be secured in vertical position even if they are full or empty. Full and empty cylinders to be segregated and marked clearly.

2. Store in Right Spaces: Never store oxygen and acetylene cylinder together in one space whenever possible. Keep them separately in well ventilated spaces. Ensure when not in use, their caps should always be on them.

3. Keep Grease and Oil Away: Control valves and fittings should be kept free of oil and grease. Never operate cylinder valves and parts with oily and greasy hands.

4. Ensure Flame Arresters Are Properly Fitted: Ensure non-return valves and flame arresters are fitted in the acetylene and oxygen cylinder lines. One flame arresters is normally fitted in the low pressure side of the regulator near cylinder and other near the torch.


5. Keep Pressure of Oxygen Higher: When performing gas welding, ensure the pressure of oxygen is always higher than the acetylene to avoid acetylene going back to the oxygen line.

6. Handle Acetylene With Care: Acetylene should not be used for welding at a pressure exceeding 1 bar of atmosphere gauge as it is liable to explode, even in the absence of air, when under excessive pressure.

7. Rectify Cause of Backfire: In case of back fire, the first priority should be to close the oxygen valve and then immediately close the acetylene valve. No operation is to be performed until the cause of backfire is rectified.

8. Handle Flashback carefully: In case of flashback or explosion of the gas pipes, first action must be to isolate the cylinder valves for both the cylinders. Further action to be taken as per ship’s fire drill procedures.

9. Ensure Proper Connections: The connections between the hose and blowpipe, and between hoses should be securely fixed with fittings to comply with Regulatory Standard.

10. Keep a Steady Watch: A regular watch to be kept on the temperature of acetylene cylinder. If the temperature is elevating, it is to be considered same as flashback or explosion situation for taking action.

11. Prevent Interchange of Hoses: Manifold hose connections including inlet and outlet connections should be such that the hose cannot be interchanged between fuel gases and oxygen manifolds and headers.

12 Replace Old and Faulty Hoses: Any hose in which flashback has occurred must be replaced with new one.

13. Handle Hoses Properly: While performing the job, the hoses should be laid properly and kept out of any moving machinery, sharp corners, high temperature areas etc. Ensure they are not dangled, knitted or tipped over.

14. Use Only Approved leak detection fluid: Only approved leak detection fluid to be used for detection of leak from hose or regulator arrangement. If it is not available, non-detergent soap (Ivory) can be used. 

15. Never Use Sealing Tape: Never use sealing tape of metal joining material to prevent leak between metal to metal gas tight joints. With an oxygen cylinder this could result in initiation of a metal- oxygen fire.

16. Never Over Tight Connections: Never try to over tight any nut of regulator connection or cylinder valve spindle to stop the leak. This can lead to damage.

17. Take Proper Steps for Maintenance: Only special tools should be used to clean any clogging in the blow pipe. Before performing any maintenance, complete system to be isolated. Never attempt repairs on pressurized oxy-acetylene equipment nor carry out any unauthorized modification on hot work equipment.

18. Use Safe Ignitors Only: Blowpipe should only be ignited with friction ignitor or other stable flame generator. Avoid using lighter as sudden flame, else blow pipe can hit the lighter body and explode.

19. Never Use Oxygen: Oxygen should never be used for ventilation, cooling purpose or for blowing dust off the surface or clothes.

20. Discard Hoses That Had Flashback: Any length of hose in which a flashback has occurred should be discarded immediately.

Last but not the least, make sure before carrying out any kind of hot work, the hot work checklist and risk assessment forms have been duly filled. Also, do not forget to follow all safety procedures while carrying out such jobs in enclosed spaces.

High pressurized gas cylinders carrying highly flammable material are a major threat to the ship and its crew. Special care and attention must therefore be taken while handling such equipment, taking into consideration all safety procedures and manufacturers’ notes.