How to avoid getting burned by hot work

Preventing losses and insuring safety

The FABRICATOR November 1998
July 26, 2001
By: Factory Mutual Engineering Corp.

Maintaining a safe work environment in facilities in which hot work, such as welding, is done can be easier said than done. Measures such as preventive safety, safety zones, and fire watches can keep employees safe and worker's comp time down

Hot work can have disastrous results in a myriad of situations:

At a metal processing plant, sheet steel became jammed in a tempering mill. An operator began using a cutting torch to remove the steel. Hot slag from the torch ignited oil deposits and oil-soaked paper towels lying around the machine. This caused exposed hydraulic and lubricating lines to weaken. Leaking oil ignited, resulting in a fierce blaze that damaged the machinery and a portion of the roof deck and framing above the machinery.

For the next three months, sheet steel had to be sent off-site for tempering until the mill could be restored to service. The total loss was estimated at more than $3 million. After the loss, management agreed to begin using a hot work permit system.

In a bay (unequipped with sprinklers) at a garage used for bus maintenance, a worker standing in a pit below a bus began welding on the vehicle's chassis. Sparks ignited combustible debris that had accumulated in the pit, and fire spread to the fiberglass bodies of several buses parked near each other.

Severe damage was caused to the bay partitions, brick walls, parked buses, overhead crane, and various maintenance tools and supplies. Damage was estimated at more than $2 million. Management acknowledged that its hot work permit system had been ignored and declared that hot work safety procedures would be enforced in the future.

At a food processor located in a 70-year-old building of plank-on-timber construction, a contractor was removing obsolete machinery and piping from a third-floor area. A member of the facility's plant engineering staff checked with the contractor early in the morning and left the area. Reportedly, the contractor had posted a fire watch with fire extinguishers.

Shortly after work with an oxyacetylene torch was begun, fire was discovered in the second floor below the pipe-cutting work area, the result of molten metal globules falling through openings in the floor.

The flooring, cartoned food stored on pallets, packaging material, and records sustained extensive fire damage, and stored food on the first floor was wet down. The estimated total loss exceeded $1 million. Management began implementing the hot work permit system shortly thereafter for both employees and contractors.

At a university, members of the theater department were fabricating props for an upcoming performance. The work included welding of metal parts. Later that evening, a smoldering fire was discovered in an air handling duct in the prop room. The fire was extinguished by a dry-chemical extinguisher.

An investigation revealed that welding sparks had fallen into a floor-level duct opening and ignited sawdust accumulations inside the duct. While the university's maintenance department was required to follow the procedures and precautions of a hot work permit system, other departments, such as the theater department, were not. After this incident, university officials instituted a new policy requiring the hot work permit system to be used throughout the school.

These are just a few examples of the hundreds of hot work losses that occur every year in a variety of locations. They reflect the reality that cutting, welding, and related hot work will probably be conducted at one time or another in nearly every manufacturing and nonmanufacturing facility. The potential hazards cut across all types of organizations, and those directly responsible may be a facility's own workers or a contractor's employees.

What Is Hot Work?

To better guard against disastrous hot work fires, fabricators need to understand what hot work is. Hot work is not just cutting and welding. It is any temporary maintenance or renovation operation producing flames, sparks, or heat. Examples include cutting, welding, brazing, grinding, sawing, soldering, thawing frozen pipe, and applying roof covering or sealing plastic shrink-wrap by torch.

The sparks and molten globules thrown off by hot work are uncontrolled ignition sources that can fly and roll a considerable distance. They will likely start a fire if they fall on combustible material, and that material is not always visible to the person performing the hot work.

Cutting into a metal wall has caused ignition of hidden combustible insulation. Also, anything combustible on or close to the other side of the wall is likely to ignite after heat is conducted through the wall for a period of time. (The flame of an oxyacetylene torch can reach up to 6,000 degrees F [3,316 degrees C].)

Hot work on vessels or tanks has led to fires and explosions when flammable residual deposits, vapors, or gases were suddenly ignited. Some fires have started as a result of poorly maintained hot work equipment, such as leaky gas hoses and connections.

The Loss Record

Is hot work a serious problem from a fire-safety perspective? Consider a recent study of hot work fires and explosions. Over a five-year period, 267 fires and explosions were reported at participating locations, for a gross total of $361 million, or an average loss of $1.4 million per incident. Some incidents exceeded $50 million.

Who is performing the hot work that results in a loss? Another study revealed that contractor's personnel were involved in 59 percent of the losses; the facility's workers were involved in 41 percent. The average loss for both groups was similar.

Another study of 616 losses in which the type of tool was reported showed 539 losses caused by a cutting or welding torch; next in order were plumbers' and painters' torches at 37 losses.

Main plant buildings are not the only targets of hot work fires. Ancillary structures such as cooling towers have also been involved. Combustible construction (plastic fill, plastic drift eliminators, wooden framing) has been ignited by careless hot work; losses in some cases have approached $1 million. Conveyors and off-road vehicles have also been destroyed by hot work accidents.

Avoiding Hot Work

The dangers of hot work are obvious, and in many cases a safer alternative can be used. For instance, cutting can be performed with hand or electric saws or pipe cutters. Mechanical joining methods such as nuts and bolts, screwed fittings, or couplings can be used. Hand filing is an option instead of grinding, and threaded pipe is an alternative to welded or soldered pipe.

Under the following circumstances, hot work must not be conducted:

  1. In areas housing hazardous processes involving flammable liquids, gases, and dusts that cannot be shut off
  2. In areas in which concentrations of flammable vapors, gases, or dusts cannot be eliminated
  3. On walls, ceilings, or floors having combustible facings or combustible insulation
  4. On equipment having combustible lining
  5. On metal piping and ducts that pass through combustible construction to which they will conduct heat
  6. Near combustible storage that cannot be relocated or covered completely with a fire-retardant cover

In general, hot work should not be permitted in situations that do not allow the use of all of the critical precautions of a hot work permit system (extinguishers, charged hose, a fire watch, etc.).

Safety Starts at the Top

Control over day-to-day hot work projects and prevention of hot work fires requires the establishment of a chain of command and responsibility. The seriousness of hot work hazards demands that policies and procedures be supported from top plant management.

A written policy is needed to express management's expectation that proper precautions and procedures be followed during hot work. This policy must be mandated both for staff and for contractors being hired.

An effective hot work policy requires some effort and time: relocating storage, shutting down a process line, setting up fire-retardant tarpaulins, wetting down a floor, removing oily deposits. However, the costs involved are but a small fraction of the potential losses to buildings, processes, and customer confidence if careless hot work results in a devastating fire or explosion.

Managers cannot surrender their authority to a contractor hired to do hot work on their property. A contractor may be the technical expert to do hot work, but he is not likely to have a full understanding of loss prevention.

Managers should obtain references from previous customers of the contractors they are considering. Discussing the planned work with the contractor will also allow them to get a sense of the contractor's expertise and understanding of the possible hazards, especially as they relate to the building and occupancy where the hot work will be conducted.

A "Hot Work Information and Responsibilities" letter can be sent to the contractor a few days before work is scheduled to begin. Bids and contracts should have similar information. All contracts should be insured, and "hold-harmless" clauses should not be signed. Managers need to make it clear that the contractor must work according to the company's policies and regulations, and that violations will be grounds for dismissal.

The Hot Work Permit

The hot work permit is not intended simply as a record to be filled out after a job is finished; it tracks each step of a hot work job and serves as a guide as well as a warning tag.

The permit is not meant to be left with the workers. Rather, it remains under the control of a fire safety supervisor, who, before signing the permit, ensures that initial precautions have been taken and discusses exactly what the work will consist of with the hot work operator and fire watch. One part of the permit is displayed prominently at the work area; the other part remains with the supervisor.

Before the permit is issued, however, the supervisor must first consider alternatives to hot work, depending on the nature of the job. If hot work is indeed necessary, then the specified precautions on the permit are taken. A summary of these precautions follows.

Protection in Place. If automatic sprinkler protection is provided for the area, it should be checked for proper operation. Sprinkler protection indicates the presence of either combustible contents or combustible construction--all the more reason to conduct the hot work with great care.

One or more portable extinguishers should be full and in working order. Depending on the amount of combustibles in the area, a charged fire hose should also be ready. The fire watch should be trained to use both.

Both the hot work operator and the fire watch should know how to sound the alarm; they should know where the nearest pull box and telephone are located.

The 35-Foot Safety Zone. Within 35 feet (11 meters) of the hot work in all directions is a critical area that must be kept clear of all combustibles. Combustible flooring should be shielded with wet sand, fire-retardant tarpaulins, or sheet metal. The area should also be cleaned, especially of oily deposits and trash.

Storage or other combustibles that cannot be moved out must be covered. Duct openings should be blocked, because ductwork provides an easy path for sparks to spread to other areas of the facility or to ignite deposits or linings within the ductwork. Openings in exposed walls, floors, and ceilings should also be covered with noncombustible or fire-stop material.

If the hot work will be done on a wall, combustibles on the other side should be moved. When hot work is planned at a height, such as on building framing, the ceiling, or the underside of the roof, a fire-retardant covering should be spread under the hot work.

All doors should be closed, with no significant gap at their bottoms or sides. Sparks have been known to roll under a closed door that was not hung close to the floor, igniting combustible material outside the hot work area.

The alternative to the 35-foot rule is to have a temporary or permanent area dedicated only to hot work. Such an area should be screened or partitioned off from the rest of the facility with noncombustible construction, but it cannot be allowed to become a convenient temporary storage area.

Fire Watch. The fire watch plays a very important dual role: to prevent fire and to respond to fire if it occurs. The fire watch must stay near the person doing the hot work, making sure, for example, that the work area remains free of combustibles, that tarpaulins are not moved, and that the fire door remains closed. The fire watch is ready to sound the alarm and use an extinguisher or fire hose if a fire starts.

The fire watch is a critical part of the hot work permit system and cannot leave the area while the work is being done, because the hot work operator is often too preoccupied with the work to personally monitor other safety aspects in the area.

After the work has ended, the fire watch should check the work area and adjacent areas (on the same floor as well as the floors above and below the work area) at regular intervals for one hour and then sign the permit.

The hot work area should continue to be checked over the next three hours. This may be done by the fire watch, a trained alternate, a guard who makes regular rounds through the area, or a designated conscientious worker from a nearby area. Finally, the fire safety supervisor visits the work area one more time and then signs and files the permit.

Why should the work area be checked well after the hot work has ended? In many loss cases, fires started with smoldering combustion in a concealed spot and were discovered two or three hours later, after open flame and volumes of smoke had developed.

Hot Work Losses Are Preventable

Hot work losses can be prevented by trained, conscientious people. A hot work permit by itself will not prevent a loss. Too many times, where permit systems are reportedly in use, some aspect of the permit is skimped on or bypassed entirely. The permit is a tool to be used conscientiously by those who supervise the hot work and those who are actually involved with it.

A financial and personal commitment is needed from senior management to demonstrate support for an effective hot work safety system. Management must insist that all involved personnel be educated in hot work hazards and how best to avoid them, that responsibility and authority be assigned to specific individuals to supervise and conduct the hot work in a safe manner, and that safeguards specified on the hot work permit be strictly observed, even if regular operations must be briefly suspended.

Reprinted with permission from The Record . The Magazine of Property Conservation, Volume 75, #1. ©Factory Mutual Engineering Corp.

Factory Mutual Engineering Corp.

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The FABRICATOR is North America's leading magazine for the metal forming and fabricating industry. The magazine delivers the news, technical articles, and case histories that enable fabricators to do their jobs more efficiently. The FABRICATOR has served the industry since 1971.

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