Work Permits and incident case study in the fertilizer industry

Work Permits and incident case study in the fertilizer industry

Work permits are absolutely crucial to the safe operation and maintenance of process facilities. They can be divided into three categories: general, hot work and confined space entry. Permits are signed by both the operations and maintenance personnel involved in the work, and by their supervisors. The permit will have the following features:

  1. A clear and precise description of the work, including its location, the equipment to be worked on, the tools and equipment to be used and the work methods to be employed. The description often requires other documents to be attached to the permit, such as job hazard analyses, method statements, isolation lists, drawings or sketches.
  2. A list of the preparations that must be made, including mechanical and electrical isolation, clearance of process materials by draining, venting, flushing, purging or ventilation, gas and/or dust testing to confirm that the equipment is free of any flammable, toxic or asphyxiating gases.
  3. Description of the hazards remaining. These may include residual process materials, pressure, temperature and physical hazards arising from the location or work to be carried out.
  4. Additional precautions to be taken during the work such as the use of personal protective equipment, further gas testing and additional monitoring.
  5. Precautions to be taken at shift handover.

 

GENERAL WORK PERMITS

General work permits are issued for all work that does not involve the use of open flames, hot surfaces, or entry into confined spaces. They cover tasks such as the following:

  1. Work in areas where electrical cables, telephone cables or pipelines run above or below ground;
  2. When scaffolding or cranes are to be used in the vicinity of in-service equipment;
  3. Excavation work, particularly if shoring is involved (some excavation may count as confined space work);
  4. The use of radiation such as X-rays; and
  5. Whenever flammable or toxic gases, vapors, oils or chemicals are present.

 

Issuance of permits

Before the permit is issued all hazards associated with the work should have been identified, and controls put in place. The person who issues the permit is different from the permit holder. A person cannot issue a permit for themselves because one of the objectives of the system is to make sure that a second, qualified person critically reviews the hazards and the proposed controls.

If a contractor is the permit holder, then the permit should be issued by a qualified person from the host company.

At least two copies of the permit are needed, one to be displayed at the work site, and the other to be held at the issuing point. The copy at the work site should be available for reference at any time by any member of the work team.

The issuance of a general work permit will normally require that the following steps be carried out:

The person in charge of the work reviews the hazards identified in the pre-job plan, and states what safety precautions must be followed during the course of the work. These can include PPE, gas retesting, continuous gas monitoring, spark containment, and the use of fire extinguishers. These conditions are noted on the work permit.

Management approves the permit for a specified time period.

Typically, a work permit is valid for one work crew. At shift change, or at the start of work the next day, the permit must be re-issued.

 

Changes in conditions

The permit should specify the action to be taken in the event of:

  1. The specified equipment or tools to be used not being available.
  2. Changes to the type of work, e.g., the need for hot work when such work had not been in the original plan.
  3. Changes in process conditions such as an unexpected release of gas from a nearby flange.
  4. A gas alarm or emergency in the area.
  5. Significant changes in the weather.

 

When events such as these take place, the normal process is to stop the work and to refer the permit back to the permit issuer. He/she will reassess the work and conditions and either re-issue the permit or issue a new or amended permit.

 

Multiple work permits

If two or more jobs are being carried out on the same piece of equipment or in the same area the chance for confusion as to which permit applies to which controls arises.

Failure to control multiple permits was a major factor in the Piper Alpha incident – two permits were open on one compressor. When the first job was finished, its permit was closed, and the compressor was started, even though the machine had a missing blind flange associated with the second job.

A display board at the permit issuing point is an effective means of maintaining an overview of all the work under permit control and of the potential interaction between jobs. Such a board also facilitates communication at shift handover.

 

HOT WORK PERMITS

Hot work involves the use of flame-producing equipment, such as welding or cutting torches, or the use of equipment that can create sparks, such as can occur when metal is being cut or hammered.

Hot work is potentially dangerous for the following reasons:

 

  1. It provides a source of ignition that could ignite a vapor release from another location.
  2. The person doing the hot work may cut through the wrong line or burn a hole in the wrong piece of equipment. This could lead to the release of hazardous chemicals or cause a fire or explosion.
  3. The person doing the work could be burned by the equipment that they are using.
  4. In confined spaces, the hot work itself can create a harmful atmosphere, leading to the possibility of a worker being overcome by fumes.

 

A Hot Work Permit is needed whenever the work involves open flames, arc welding, electrically sparking equipment or other ignition sources within a predefined distance, such as 15 m, of facilities handling flammable or combustible materials.

A Hot Work Permit includes all the elements of a General Work Permit. In addition, the following checks should be carried out before the permit is issued:

  • Inspection of the site;
  • Vapor testing; and
  • The availability of fire-fighting equipment.

The following questions should be considered as the hot work permit is being prepared:

  • Can the work be done in a less hazardous area?
  • Can the job be done by cold work?
  • Has the site been inspected by a responsible individual?
  • Have pipelines or equipment that may release flammable or combustible materials been blinded off or disconnected?
  • Are pipelines or equipment to be worked on vapor-free or vented?
  • Have process liquids been drained from all low points?
  • Are bleeders open and unplugged?
  • Have openings to sewers and underground drains within 15 meters of the work been sealed?
  • Are operating activities (e.g., venting, sampling) likely to release flammable vapors or liquid to the atmosphere within 15 m of the hot work area?
  • Are flammable vapor tests necessary?
  • Are fire hoses and portable extinguishers available?
  • Are there any chemicals in the area that could be a hazard to firefighters?
  • Is it necessary to redirect venting from relief systems away from the hot work area?
  • Are workers in adjacent areas and affected plants aware that the work is going on?
  • Will working conditions remain safe for the duration of the job?
  • Do the fire watch personnel know what to look for and what to do if hazardous conditions arise?
  • Do they know how to use emergency equipment properly?
  • Are radio communications between the fire watch and the control room/supervisor needed?
  • Are combustible materials such as wood or rags present?
  • Are fire screens and blankets required to contain sparks and slag?
  • Are high-velocity, high volume, electrically classified fans required to direct potentially flammable vapors away from the area?
  • What is the chance that wind-borne hot particles could drift outside the hot work area and what impact could they have?

 

CONFINED SPACE ENTRY

A confined space is large enough for a person to enter but has limited openings for entry and exit and is not intended for continuous employee occupancy. Confined spaces include, but are not limited to, storage tanks (fixed and floating roof), towers, drums, boilers, furnaces, sewers, ventilation and exhaust ducts, manholes, pipelines, and excavation pits. A person is said to have entered a confined space if they break the plane of the confined space portal with his/her face. Therefore, it is not permissible, for example, to take a breath and to put one’s head into a vessel for a quick look.

Before a person can enter a confined space, conditions such as the following must be met:

  • It must be shown that the work cannot be accomplished from the outside.
  • The oxygen content must be in the range 19.5–23.5%.
  • The flammability level must be below 10% LEL.
  • There are no toxic gases in the confined space.
  • The space does not contain grain, sand or other solid material that could flow and engulf a worker.

 

The past incidents tell us that there is a big difference between checking a piece of equipment to see if everything is ready or checking it to see if anything can possibly go wrong. The extra amount of time it takes to eliminate every possibility of an accident is a small price to pay to save your people from pain, anxiety, or worse.

Case study (based on a paper presented at AICHE Ammonia Safety symposium in 1974):

The Borger Ammonia Plant had been shut down on the 11th of the month, and the repairs requiring the plant to be shut down had been completed. On the 15th, while the plant was in start-up, two maintenance men were assigned to replace the packing in the steam heated MEA reboiler.

This reboiler has lean MEA on the tube side, with 50 Ib. steam entering the steam chest at the top on the shell side. The condensate line leaves the steam chest near the bottom, rises several feet and passes on to the condensate collection header. The lower portion of the tube bundle has a floating head connection which passes through the steam chest outer bottom head through this afore-mentioned packed joint. The two maintenance men contacted the operations supervisor for a work permit before working on the reboiler.

The inlet steam block valve to this reboiler had been closed at the time of the shut down and all of the condensate valves blocked and the reboiler steam-side drained. The supervisor checked that the steam valve was still closed, and had some operators pull down on the valve to verify that it was closed. The drain was checked and was found to still be open, as was the vent on the steam chest.

The maintenance men donned protective equipment and set up a scaffold so that they could work at the packing gland without any risk of strain or fall.

They loosened the nuts holding the packing gland in place and knocked the gland follower down with a tool. When this happened, about 50 gallons of boiling hot water suddenly rushed out on them, drenching one of them thoroughly and lightly splattering the other one. Both jumped to the ground and nearby workers stripped their clothes off and washed them with cold water. The worker who had received the brunt of the hot water suffered second and third degree burns over his face, upper torso and arms. The other maintenance man was not burned and returned to work. The injured man lost 26 days of work as a result of this accident.

The investigation following the accident revealed that the steam block valve was leaking a small amount of steam, even though it was closed. This leakage was not sufficient to develop any pressure on the steam chest, but did accumulate hot water in the floating head shell immediately above the packing joint, just below the condensate outlet.

The open drain permitted any excess accumulation of water to be drawn off so as to give the appearance that the exchanger was empty. To eliminate this problem, a small drain has been installed on the floating head shell immediately adjacent to the packing joint, so that any water accumulations may be drained before the packing joint is loosened.

 

References:

  1. Ian Sutton, Process Risk and Reliability Management, 2010 Elsevier Inc. P389-393
  2. Accident Involving Hot Water, AICHE Ammonia Safety Symposium 1974
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