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Standards Division

FIRE PROTECTION ANALYSIS CONSIDERATIONS

Richard Fredenburg, LP-Gas Engineer

[NOTE: This information is for a fire PROTECTION analysis, not for a fire SAFETY analysis. Click here to be taken to information about a fire safety analysis.]

There have been a number of questions about covers over, and enclosures around, LP-Gas tanks. These may have been put in place as weather shelters or even as a screen for appearances and may not appear to be a problem to the owner or operator of the tank. These structures may be allowed, providing they meet certain requirements.

CONTENTS OF THIS WEBPAGE

ENCLOSURES AROUND OR OVER TANKS

The 2014 Edition of the LP-Gas Code (NFPA 58) has the following sections that address having enclosures around or over propane tanks:

  • 6.4.5.1 Structures such as fire walls, fences, earth or concrete barriers, and other similar structures shall not be permitted around or over installed nonrefrigerated containers unless specifically allowed.
  • 6.4.5.2 Structures partially enclosing containers shall be permitted if designed in accordance with a sound fire protection analysis.
  • A.6.4.5 The presence of such structures can create significant hazards, such as the following:
    (1) Pocketing of escaping gas
    (2) Interference with application of cooling water by fire departments
    (3) Redirection of flames against containers
    (4) Impeding the egress of personnel in an emergency

At the heart of determining if a tank can be enclosed is a requirement for each such location to be “specifically allowed.” This means that the Standards Division has issued a letter stating that the enclosure for a tank, at a specific location, has been approved and is permitted. The basis for that approval is a fire protection analysis. Some guidance for this can be found in the annex of the LP-Gas Code, in section a.6.4.5., with some further explanation here. There is also a suggested format for the fire protection analysis to be sure all the points we need to consider have been addressed.

Specific approval for an enclosure over or around a tank should be requested prior to installation, as operation of the tank is a violation without the approval. It may also be requested after an inspection as a way of correcting a violation for an enclosure, however there is the risk of it not being approved and the possible expense of moving the tank or the enclosure. Either way, the request must clearly ask for permission to either install an enclosure or to allow an existing enclosure to remain for a tank at a specific location. In addition, the letter should be available for the inspector’s review during an inspection.

If you have, or want to install, an enclosure or cover over or around a propane tank, we offer the following explanation on the potential significant hazards, as listed above, for you to consider:

(1) Pocketing of escaping gas
Pocketing of gas is generally caused by lack of ventilation or by low places that are blocked from airflow. A cover over a propane or butane tank will not cause pocketing of gas, but it could hinder circulation by blocking breezes or winds. Ensuring that at least 50% of the perimeter of the tank is open will meet the minimum requirements of the code, assuming there are no other features that foster pocketing. Surrounding a tank site with chain link fencing does not require a fire protection analysis as long as the ventilation is not hindered by slats in the fencing or other methods to screen the tank from sight.

(2) Interference with application of cooling water by fire departments
The most common cause of interference with application of cooling water is covers over tanks. Tall walls can also interfere. Consideration must be given to availability and direction of access routes by emergency responders. Directions of approach accessible to emergency responders must not have interfering features. If a cover is sufficiently high, water may be able to reach the tank. This must be coordinated with emergency responders. Their written statements of being able to apply cooling water on all parts of the container are required and play a vital part in the fire protection analysis. A statement that they can fight a fire on the site is not enough. They must clearly state that they can apply cooling water to the tank.

(3) Redirection of flames against containers
Redirection can be caused by a number of features. A cover over the tank will likely redirect the discharge from a relief valve back down to the vicinity of the tank. Such discharge may fully engulf the tank in flames. Other features that can redirect flames are walls, cabinets, barriers, and nearly any object near the tank or piping. Piping can sometimes break in a most inconvenient manner, discharging the fuel toward the tank, as evidenced by a BLEVE in Iowa several years ago. While no enclosure contributed to this incident, it demonstrates the concern of flames directed at the tank. (See the section on relief valve discharge requirements for more detailed commentary on relief valve discharge.)

(4) Impeding the egress of personnel in an emergency
Enclosures, usually fencing, around tanks provide security. They can also trap people. Enclosures that are large or contain transfer operations are required to have at least two means of egress, ensuring one is available should something block the other. This is the reason we require that enough gates be unlocked during operations in a fenced area. A gate does not count as a gate if it is locked closed. Other enclosures can inhibit dispersal of released LP-Gases and can impede egress of personnel. Jersey barriers linked together are an example, as are privacy fences. Care must be put into the design of these structures to ensure safety.

When would an inspector consider this situation a violation?

An inspector would note a violation if they determine that any structure present covers the tank, if the perimeter of the tank is enclosed for more than 50%, or if there are other issues with an enclosure around the tank. "Cover" is the term used in this report to refer to any enclosure over a tank or dispenser. It can include any device or structure over a tank, including a roof, a canopy, a tent, a building, etc. Of course, if there is an approval letter for the structure on file, it would be approved on the inspection.

Tanks enclosed for less than 50% of their perimeter will not normally be cited for a violation for an enclosure around the tank. Five sections in the LP-Gas Code indicate the intent to limit enclosures around potential discharges to no more than 50% of the perimeter. They are:

  • 6.3.4.1 (a requirement for cylinders)
  • 6.8.5.1 (a requirement for discharge from regulators)
  • 6.25.3.3 (a requirement for dispensers)
  • A.3.3.79 and A.6.5.1.1 (both statements in the non-regulatory annex about container-enclosing berms and enclosures around point of transfer).

Thus, it is presumed that enclosures of less than 50% of the perimeter will not hinder the ventilation of the area of the tank or present a hindrance to application of cooling water to the tank.

Please note that there are some sites with very tall walls that could prevent the application of cooling water. The inspectors could cite these locations if they feel that emergency responders may not be able to apply water, even if a site is not enclosed for more than 50% of the perimeter. This could be resolved through a visit and documentation from the local fire marshal that they can provide cooling water to the tank.

NOTE: The concern about an enclosure over or around a tank is the application of cooling water to the tank. It is not "fighting a fire" at the site. Do not try to extinguish a propane fire until the source of the fuel can be stopped. In the meantime, application of cooling water to the tank can delay or prevent failure of the tank.

Can my cover/enclosure be “grandfathered”?

The requirements presented here have been in the LP-Gas Code since they were added in the 1983 edition. There may be a small number of installations that predate that edition and a claim for retroactivity (grandfathering) may be made for those sites. Such a claim would have to be for the same container that was installed prior to 1983. Anything newer, including a different container at that site, would fall under the requirements added in 1983 and a claim of retroactivity could not be made.

RELIEF VALVE DISCHARGE REQUIREMENTS

Another consideration, especially regarding covers over tanks, is the 2014 Edition of the LP-Gas Code (NFPA 58) sections that address the requirements for relief valve discharge from LP-Gas tanks:

  • 6.7.2.3 Pressure relief devices on the following ASME containers shall be so installed that any gas released is vented away from the container upward and unobstructed to the open air:
    (1) Containers of 125 gal (0.5 m3) or more water capacity installed in stationary service
    (2) Portable storage containers
    (3) Portable tanks
    (4) Cargo tanks
  • 6.7.2.7 Pressure relief valve discharge on each container of more than 2000 gal (7.6 m3) water capacity shall be directed vertically upward and unobstructed to the open air.

The requirement for the relief valve to discharge upward and unobstructed to the open air is clear and straightforward. Implementation is more complicated if a cover over the tank is desired.

The relief valve discharge must not be obstructed by a cover. If it is obstructed, it may redirect the discharge back down onto or around the tank. This redirected discharge is very flammable, having mixed with large amounts of air very quickly after its release. A source of ignition is very likely to be present, as the reason for the relief valve discharge may be the result of the tank being heated by a nearby fire. Discharge from relief valves under a canopy will not be allowed for any reason, unless it is piped through the canopy, as obstruction of the relief valve's discharge is prohibited by the LP-Gas Code. Discharge must be upward and unobstructed to the open air, as required by section 6.7.2.3.

Having an opening in the cover appears to be one way to meet the requirement, but knowing how large an opening is a problem. The farther the cover is vertically from the relief valve, the larger the opening must be, as the discharge plume gets wider the farther from the valve discharge opening it goes. Our attempts to determine the shape of the discharge plume have not been successful. Manufacturers contacted by us declare that they do not know the size and shape of the discharge form their relief valve.They have provided no information to help determine the size of an opening in a cover for unobstructed relief valve discharge. The width of the discharge can be observed in various photos and videos of the flaming discharge, but knowing the manufacturer and model of the valves involved is practically impossible. Direct measurements have not been made. A fire protection analysis that includes a hole in the cover or credit for horizontal separation between the relief valve and the cover would need to include technical justification and support for the size and location of the hole or for the separation.

Piping the discharge through the cover is permitted in some cases. If the relief valve discharge opening has threads for a stack or coupling, then a stack may be added to pipe the discharge through the cover. A practical limitation exists for this for tanks of 4000 gallons or smaller. Virtually all of these tanks must have internal spring-type relief valves. (See the LP-Gas Code Table 5.7.4.1(D), Part D, column 2.) Relief valves for tanks of 1000 gallons or smaller typically do not have threads for attaching a stack or coupling. Also they have not been listed or tested for properly discharging through discharge piping. Therefore, if discharge piping is attached to the outlet or placed over the outlet, the listing for these valves is violated. No discharge piping is allowed for relief valves with no threading for discharge piping. No tank may be fitted with an external relief valve if the requirements of the above reference are violated.

With the unknown concerns of the shape of the discharge plume and the restriction against discharge piping for many valves, covering any part of a tank brings up questions about meeting the requirement for unobstructed discharge. Any request for a cover over a tank must address and resolve these questions.

This concern about separation of the cover from the relief valve is still being explored. Suggestions for how to provide justification for horizontal separation distances and opening sizes are encouraged.

Can my tank’s relief valves be “grandfathered”?

The requirements presented above have been in the LP-Gas Code since before the 1969 edition. There may be a very small number of installations that predate that edition and a claim for retroactivity (grandfathering) may be made for those sites. For retroactivity to apply, the same container and the same cover must have been in place continuously since before 1969.

FURTHER EVALUATION OF COVERS RELATING TO THE REQUIREMENT FOR A FIRE PROTECTION ANALYSIS AND A VIOLATION FOR RELIEF VALVE DISCHARGE

In an effortt to help inspectors determine when a fire protection analysis is required and when a violation for obstructing the relief valve discharge is present, the following direction was developed:

  1. If the entire pressure relief valve (PRV) is not under a cover, there is no violation for obstruction. (or, if any part of a PRV is under cover, it is an obstruction violation) Except see #5.
  2. If the cover extends over the end of tank to the first weld (attaching head to shell of tank) or less – no fire protection analysis (FPA) is required (no violation). The cover is considered incidental.
  3. If the cover is over the end of tank and past the first weld – FPA required (violation)
  4. If the tank and PRV are under a cover – FPA required and violation for obstruction of PRV
  5. If the tank is under a cover but there is a hole in the cover over the PRV – The valve will be considered obstructed and a FPA is necessary as well.

Explanation for #5: The PRV needs to be moved beyond the outside perimeter of the cover. Since we don’t know how big the hole should be above a PRV, there may be some liability in allowing it, though we will be willing to review any information and data provided. We have seen some that have removed the entire section(s) of the cover immediately above the entire tank, leaving the rest intact. That is acceptable as neither the tank nor the PRV are under a cover. Any ribbing or supports still in place from removing that section of the cover would be considered incidental.

SUGGESTED FORMAT FOR THE FIRE PROTECTION ANALYSIS

The following format for a fire protection analysis would satisfy the code requirement and provide enough information for us to consider the request:

  1. Location of the site – Name and physical address of site.
  2. Drawing and/or photos - A drawing or photos are not specifically required for the fire protection analysis, but may aid in the understanding of the site and situation by the person reviewing the analysis.
  3. Evaluation for potential of enclosure to allow pocketing of gas – Determine if the enclosure hinders ventilation or has low points that foster accumulation of gases. Any structure closed for more than 50% of its perimeter will require technical justification that gases will not pocket and will disperse.
  4. Evaluation of sources of ignition
    1. Demonstrate that there are no electrical sources of ignition or other electrical devices that do not comply with Table 6.23.2.2 (LP-Gas Code, 2014 edition).
    2. Demonstrate that there are no other sources of ignition (spark-producing tools, lit smoking materials, stored or accumulated flammable materials, etc.) present or brought into the area regularly.
    3. Description of signs and administrative controls to prevent introduction of sources of ignition may be appropriate.
  5. Evaluation of releases from the tank and piping – Consideration of the following concerns and how they have been assured to comply. (It is intended that this item be evaluated by someone familiar with propane containers and equipment; not emergency responders.):
    • Relief valve concerns:
      1. Is the discharge from the relief valve(s) directed upward and unobstructed to the open air?
      2. Is placement of the relief valve relative to a cover over the tank such that the valve discharge cannot be deflected?
      3. If piping is used to direct relief valve discharges through the cover, is the discharge opening of the relief valve designed and intended to have discharge piping?
      4. If piping from the relief valve has been used, has it been designed so that it does not restrict the flow amount from the relief valve?
    • Other piping concerns:
      1. Is piping routed so that a break would not direct the escaping fuel toward the tank?
      2. Have other features that would redirect escaping fuel or flames toward the tank been eliminated?
  6. Evaluation of enclosure to hinder application of cooling water – The local emergency responders (fire department) or fire marshal must provide a written statement that enclosures over or around the tank(s) will not hinder their application of cooling water to the tank(s). (A statement that they can fight a fire at the site is not sufficient.)
    • The statement must include:
      1. business name and address of the site evaluated
      2. date
      3. evaluator printed name
      4. evaluator signature
      5. evaluator position
      6. contact information for the fire marshal, fire chief, or other responsible fire service official.
      7. Statement that enclosures will not interfere with application of cooling water to tank(s).
      8. Use of the evaluator's organization letterhead would be beneficial but is not required.
    • Consideration must be given to the:
      1. Availability of water for applying to the tank and for fighting other fires on the site
      2. Height of the cover and clearance between tank and cover
      3. Height of walls near a tank
      4. Access directions
      5. Any other features deemed important.
  7. Evaluation of impeding egress of personnel during an emergency – Does the enclosure meet the egress requirements of section 6.19.4.2? Are there impediments other than a fence that could hinder egress?
  8. Documentation details– Include the name of the submitter and position within the organization, date completed, and contact information.

CHECKLIST FOR FPA

We evaluate FPAs to determine if the above items have been properly addressed, using a checklist to do so. You may get a copy of this checklist for your use before you submit the FPA to help ensure that you have considered all items. Access the checklist.

SUBMITTAL

Submit your request for specific allowance of the enclosure and the fire protection analysis to the Standards Division office, not to the inspector.

  • Mail it or send it by a delivery service to NCDA&CS, Standards Division, Attention: LP-Gas Engineer, 2 W. Edenton Street, 1050 Mail Service Center, Raleigh, NC 27699-1050 or
  • E-mail it to Standards@ncagr.gov, including the fire protection analysis as an attachment as either a Word document or as a pdf file.
  • Please do not send by facsimile as they can be difficult to read.

Last updated July 28, 2017

 

NCDA&CS Standards Division, Stephen Benjamin, Director
Mailing Address:1050 Mail Service Center Raleigh, NC 27699-1050
Physical Address: 2 West Edenton Street, Raleigh, NC 27601
Phone: (919) 707-3225; FAX: (919) 715-0524



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