Occupational Health & Safety

Controlling Hot Work Fire Hazards

It's highly advisable to use a hot work permit system for all hot work operations outside the designated area

Hot work continues to be a leading cause of industrial fires, consistently in the top five across all industries, and it has been responsible for many of industry's most severe fire losses. Hot work is often synonymous with welding and cutting but also includes any work activity with potential to produce ignition sources or excess heat, such as burning, brazing, grinding, soldering, thermal resistance heating, or torch applied roofing.

Sparks and molten material from hot work can be scattered more than 35 feet during welding, cutting, and grinding. These sparks and slag are typically at a temperature above 1,000 degrees F when thrown from the hot work operations—a temperature which can easily ignite paper, wood, flammable liquids, vapors, and many other combustibles if they are allowed to come into contact. While designated hot work areas should have a 35-foot clear radius of combustibles typically maintained, there are very few areas in the average facility that are always clear of combustible material 35 feet in all directions from a given point. If combustibles are not relocated, wet down, or protected with welding curtains or blankets, the hot sparks and slag from welding can easily lead to ignition.

Additional fire hazards from hot work include:

Sparks can fall through cracks and other floor openings, thus starting fires in hidden locations.

Ducts and conveyor systems can carry sparks to distant combustibles.

Hot work done near a partition, wall, ceiling, or roof that has a combustible covering or insulation, or on walls or partitions of combustible sandwich-type panel construction, can lead to ignition.

Hot work on one side of a wall can ignite combustibles on the other side.

Hot work on pipes or other metal that is in contact with combustible walls, partitions, ceilings, roofs, or other combustibles can lead to ignition through conductive heating.

With containers and piping, there is the possibility of explosions, fires, and the release of toxic vapors or fumes.

Before Beginning

Evaluate the decision to perform hot work. The first step of the hot work management process is to determine whether the hazard can be avoided or minimized. Where practical:

Avoid hot work if possible.

Relocate the object requiring hot work outdoors or to specially designated areas that have been designed and constructed to minimize fire risk.Good housekeeping should be maintained and the area routinely audited to ensure it remains safe for hot work.

Schedule hot work during shutdowns if it cannot be avoided or relocated.

If it is determined that hot work is necessary and the object cannot be relocated to a designated hot work area, the persons requesting and those who will be performing the hot work should contact a Hot Work Permit issuing supervisor and begin the permit process.

Utilizing a Permit System

While many standards, including NFPA 51B, Standard for Fire Prevention During Welding, Cutting, and Other Hot Work, require a permit only under certain conditions, such as being unable to secure a 35- foot radius clear of combustibles, it is a best practice and highly advisable to use a hot work permit system for all hot work operations outside the designated area.

Like any other safety program, the first and most critical step in implementing a hot work permit program is a comprehensive written policy and firm management support. Employees and contractors must fully understand that before undertaking any welding outside designate areas, a permit must be obtained from an authorized supervisor and violation of the hot work policy is not acceptable. Even if a facility does not have welding equipment or trained welders and hot work would be a very seldom occurrence performed by outside contractors, a hot work policy and permit system should be in place and included in the contractor management program.

Permit Issuing Supervisors

The permit issuing supervisor's role in completing the permit is to ensure the area or equipment is properly prepared for hot work and the operation is conducted safely. Any supervisor selected to issue permits should be trained in the hazards of hot work and the site-specific hazards, such as flammable liquids, hazardous processes, and storage areas. They must understand the situations that can prevent hot work from being performed and how to interpret atmospheric monitoring results.

One of the most common errors in hot work management programs is the issuance of hot work permits from an office or other production area.To properly issue a permit, the supervisor should tour the proposed hot work area and visually verify that all permissive conditions of the permit are met. Once the permits are properly completed, there should be a copy of the permit kept with those performing the hot work— such as affixed to the welding equipment— and a copy should remain in the supervisor's office or possession during the hot work operations.

Permit Components

Permits should contain a section, preferably highlighted or otherwise set apart from the other items, saying that if any of the situations within exist, hot work cannot be performed and no permit can be issued. The permit also should include a checklist section for confirmation of general conditions. In addition to the hazards checklist portion, permits should contain a section that describes the location, nature, and time of the work and those responsible for the hot work, fire watch, and supervision. The sample hot work permit in Figure 1 provides an example of the items for the conditions checklist section:

Vessel, Container, and Piping Precautions

The heat from the hot work can release hazardous and potentially flammable fumes from materials hidden in cracks and crevices, even in containers appearing empty. Even containers and piping containing water should be considered hazardous until verified otherwise because byproducts of corrosion can result in hydrogen accumulation and potentially explosive atmospheres. Due to the potential for personnel injury, company guidelines always should be consulted for further guidance before conducting hot work on or within any vessel, container, or piping. At a minimum for property conservation, prior to applying heat to or welding on any vessels, containers, or piping, the following precautions should be included on the permit and taken when applicable:

Do not perform hot work on any equipment, drums, tanks, or other containers that have previously contained materials that could develop explosive atmospheres until they have been sufficiently purged, cleaned, and verified as non-hazardous by a qualified person.

For enclosed vessels and confined spaces, a qualified person should check the atmosphere for:

  • Suitable oxygen content (maximum alloable range of 19.5 to 23.5 percent)
  • Combustibles or reactive gases
  • Toxic gases

When working on piping, where feasible, isolate lines by capping or double-blockand- bleed valving and venting.

During and After Hot Work

Once the hot work has been approved, often the only two employees or contractors in the area are the hot work operator and the fire watch. There is no set guideline for the supervisor to remain in the area or to routinely audit areas while hot work is being performed, but it is a good practice to make periodic rounds as time permits to ensure conditions remain safe.

During hot work, the operator and fire watch must ensure the ongoing safety of the hot work operation throughout the process. If unsafe conditions develop, the operator should immediately stop the hot work operation and notify management, the area supervisor, or the permitissuing supervisor for reassessment of the situation.

Fire Watch

The fire watch, just as the hot work issuing supervisor, should be trained to understand the inherent hazards of the work site and of the hot work and ensure safe conditions are maintained during hot work operations. The fire watch should have adequate fire extinguishers and/or small hose lines available and be trained in their use. The fire watch has two principal duties during hot work operations and during the minimum 30-minute post-hot work fire watch period:

Watch for fires in all exposed areas and try to extinguish them as long as they are in the incipient stage. If the fire watch determines the fire is not within the capacity of the equipment, the fire watch and operator should leave the area and sound the fire alarm immediately.

Watch for and stop the hot work operations if unsafe conditions develop. During the post-hot work period, the fire watch may be allowed to perform additional tasks as long as they do not distract him or her from their primary duty of fire watch responsibility. When the fire watch period is completed, the fire watch should make a final check of the area, sign the permit in the appropriate location, and return the completed permit to the supervisor.

Managing Hot Work with Diligence

Ensuring proper safety in a hot work program should be done with the same diligence as an electrical and equipment lockout/tagout program. One would never open electrical switchgear or climb inside equipment capable of moving without absolute verification that it is not live and is properly locked out to prevent activation during work.

Aside from being trained on the potential serious personal injuries that can occur from not following the lockout/tagout procedures, at most facilities employees and contractors are keenly aware that violating the facility's lockout/tagout policy has serious consequences—including dismissal from the facility, in many cases. Property damage and personnel injury from hot work can be greatly reduced by managing the hot work program with the same diligence and philosophy.

Potential hot work areas should be assumed unsafe until they have been rendered safe and verified by a qualified person and/or hot work supervisor, including:

All containers, including fixed tanks and mobile containers.

All piping, regardless of type of fluid normally present.

All areas within the general facility outside the designated welding area.

Virtually all severe fires and explosions caused by hot work can be avoided with proper management of the process. All parties must understand the mutual responsibility for prevention of hot work fires and explosions and proper use of a hot work permit system, taking ownership of their individual responsibilities, which include management support, supervisors' proper use of the permit and procedures, and welders and fire watches to ensure safe practices are followed before, throughout, and after the welding process.

 

REFERENCES:
1. American National Standards Institute, Inc., 25 West 43rd St., 4th Floor, New York, NY 10036.ANSI Z49.1, Safety in Welding, Cutting, and Allied Processes, 2005.

2. NFPA 51B. Standard for Fire Prevention During Welding, Cutting, and Other Hot Work. 2009 Edition.

3. American Welding Society, 550 N.W. LeJeune Road, Miami, FL 33126. AWS F-4.1, Recommended Safe Practices for the Preparation for Welding and Cutting Containers and Piping, 1994.


This article originally appeared in the April 2009 issue of Occupational Health & Safety.

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