Protecting Cable Trays Against Hydrocarbon Fire In The Oil & Gas Industry

By Chris Dodds on 2nd March, 2015

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Protecting Cable Trays Against Hydrocarbon Fire In The Oil & Gas Industry

3M Oil & Gas 

 

The following article from 3M Oil & Gas Division follows the recent Blog by T&D's Chris Dodds where we considered the impact of sub-standard specifications in the oil and gas industry for electrical cable jointing systems in hydrocarbon installations. 

 

T&D UK would like to thank Sean Appleton (3M Marketing Manager - Oil & Gas Business) for his Guest Blog contribution on the subject of providing adequate protection to cable trays against hydrocarbon fire in the oil and gas industries. 

 

The Piper Alpha Disaster

The North Sea Piper Alpha disaster of 1988 was the worst offshore oil and gas disaster in history. Resulting in 167 fatalities with most of those suffocating in toxic fumes that developed after a gas leak set off the blasts and started a major fire. 

More recently, tragic incidents at oil and gas facilities in the US, Argentina, Venezuela and Japan have served as a timely reminder of the devastating human, financial and ecological impact of a fire. These events highlight the need for fire safety to be given prime consideration.

Pictured: North Sea Piper Alpha Disaster 1988

Piper Alpha Disaster 1988

When a fire occurs at a refinery, offshore facility or petrochemical plant, the electrical systems that serve critical areas such as control rooms, process equipment, ventilation, sprinklers, alarms and other emergency systems must remain operational.

Pictured: Workers Onboard Piper Alpha North Sea Oil Rig Were Demonised For Not Following Safety Precautions

Workers Onboard Piper Alpha North Sea Oil Rig

In particular, cables that ensure the activation of emergency shut down valves (ESDVs) must be adequately protected in order to isolate the flow of fuel to the fire, preventing further escalation of fire and explosion. 

The fire protection of electrical raceways or cable trays that act as conduits for cables supporting these process-critical functions is therefore of vital importance to operators. 

As well as mitigating against the financial implications that loss of property and disruption to ongoing production brings, a robust, well designed fire protection system can prevent catastrophic loss of life and devastating environmental impact.

A good starting point when considering the specification of such systems is the American Petroleum Industry (API) 2218, Fireproofing Practices in Petroleum and Petrochemical Processing Plants, which offers guidance for “. . selecting, applying, and maintaining fire proofing materials that are designed to limit the extent of fire-related property loss in the petroleum and petrochemical industries.”

According to API 2218, “The principal value of fireproofing is realised during the early stages of a fire when efforts are primarily directed at shutting down units, isolating fuel flow to the fire, actuating fixed suppression equipment, and setting up cooling water streams.” 

A number of options are available to operators for providing hydrocarbon fire protection to cable trays including calcium silicate boards, intumescent and ablative coatings, ceramic fibre blankets and endothermic mats.

Each of these materials has different properties, which operators should evaluate in order to select the most appropriate system for the requirements of their specific application.

Design Considerations

When specifying fire protection systems for cable tray applications, specifiers should consider a number of criteria, including:

  • The proven ability of the system to maintain circuit integrity under fire
  • Ampacity derating
  • System flexibility requirements
  • System weatherability requirements
  • Weight load capacity
  • Total system installation cost

All fire-resistant systems should be tested in accordance with industry standards in order to ascertain how the system will perform when subjected to a high intensity hydrocarbon fire.

API 2218 recommends UL1709 (or functional equivalent) as the primary standard for hydrocarbon fire testing. UL1709 reaches 1100°C within five minutes, and maintains that temperature for the duration of the test. 

API 2218 also recommends that critical wiring and control systems be protected for 15 to 30 minutes to UL1709 or equivalent testing if the control wiring is used to activate emergency systems during a fire. A reputable materials supplier will be able supply appropriate documentation to validate such testing.

Ampacity Derating

This refers to the reduction of a cable’s ability to conduct electricity and can be tested through the use of IEEE 848 Standard Procedure for the Determination of the Ampacity Derating of Fire-Protected Cables. 

The higher the level of insulation provided to a cable, the less current it can conduct without risk of damage from overheating.

Therefore, if a cable is derated by 40 percent it can only be used to conduct 60 percent of its ambient capacity.This can have major implications on design cost, footprint and overall system weight.

System Flexibility

The choice of fire protection system should reflect the existing maintenance regime and possible requirements for future cable alterations. A more fixed system will be difficult to re-enter for inspection and upgrade of cable trays. 

System Weatherability

The location and level of exposure of a cable tray can vary greatly as can the weatherability performance of fire proofing materials.

Systems exposed to high levels of liquid or vapour may require additional surface protection such as a top coat or surface cladding. UL 1709 testing includes a standard set of exposures for weatherability and chemical tolerance as part of its normal testing protocol. 

Weight Load Capacity

Weight load capacity of cable trays will have an influence on the weight, and therefore type of fire proofing materials which can be applied. 

Total System Installation Cost

Total system installation cost should be evaluated based on the total material costs, labour and installation costs, expected life cycle and the associated maintenance and replacement costs.

When upgrading existing facilities, disruption to ongoing operations as a result of system installation should also be a key consideration.

Endothermic Technology

Specifiers are increasingly turning to endothermic materials for hydrocarbon protection of cable tray
applications due to its flexibility, cost effectiveness and performance properties. The term “endothermic” describes a reaction in which the material absorbs energy from its surroundings in the form of heat.

When exposed to high temperatures, endothermic materials release chemically-bound water to cool the outer surfaces of the material and significantly retard heat transfer. 

Endothermic material is usually supplied in  ‘blanket’ or ‘mat’ form providing the flexibility for installers to wrap the material around critical areas of all types including cable trays, conduit, equipment shrouds and other electrical systems.

Unlike traditional hydrocarbon fire protection materials such as lightweight cementitious and intumescent coatings, endothermic materials require minimal preparation to install, with no need to prime or recoat the substrate.

In addition, endothermic blankets reduce the possibility of human error in mixing and application, while significantly reducing installation time, wastage and mess.

A further benefit of the system’s flexibility allows it to be installed easily and maintained with virtually no disruption to surrounding areas.

The product is also re-enterable and can be removed and reinstalled for quality inspections or future refits. 

Advanced endothermic materials such as 3M Interam Endothermic Mat (‘E-Mat’) can be used for both internal and external applications and offers excellent performance in many fire scenarios, including large hydrocarbon pool fires in accordance with UL 1709 (ASTM E 1529).

 

Conclusion3M

3M E-Mat has been used extensively around the world for over 30 years and is ideal for effective fire safety solutions for both offshore and onshore energy environments. As a major hazards industry, reducing the number of dangerous occurrences and improving safety standards should be key priorities. The continuous development and application of new technologies that can improve safety performance is therefore vital. 

 

3M Interam Endothermic Mat E-5A-4

Flexible mat with endothermic technology that, when exposed to high temperatures or flame, releases chemically bound water to slow heat transfer and help protect critical electrical and structural components from fire.

3M Interam Endothermic Mat E-5A-4 Product Features 

  • Provides up to 4 hour fire protection for structural steel applications1 in accordance with ASTM E 119 
  • Provides up to 3 hour fire protection for electrical circuit applications1,2 in accordance with ASTM E 1725 
  • Provides protection against large hydrocarbon pool fires in accordance with ASTM E 1529 (UL 1709) 
  • Chemically-bound water helps cool protective item(s) in the event of a fire 
  • Non-flame supporting
  • Low-smoke evolution 
  • Flexible – can be installed on complex shapes and around corners 
  • Easy-to-cut for various shapes and sizes 
  • Non-corrosive 
  • For use in new or retrofit applications 
  • Easy-to-clean

3M Interam Endothermic Mat E-5A-4

Protecting Cables Against Hydrocarbon Fire Within The Oil & Gas Industry

Protecting Cables Against Hydrocarbon Fire

Video: 3M Interam Endothermic Mat | E-5A-4 | Cable Tray Installation

 

 
  • Further reading

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API2218 - Fireproofing Practices In Petroleum & Petrochemical Processing Plants





Category:  Cable Containment LV HV

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