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The need to protect control cables and control valves from fire is one of the important requirements in refineries and other fire-prone locations. And for this requirement, we can have multiple options, including fire blanket systems, calcium silicate boards and flexible pads that absorb heat in the event of a fire. All available cable fire protection solutions have distinct advantages, and refineries must weigh the pros and cons of each solution to determine which one is suitable for application.
"Fire Protection Specifications for Petroleum and Petrochemical Processing Plants" provides guidance for "the selection, application and maintenance of fire protection materials designed to limit the extent of fire-related property damage in the petroleum and petrochemical industry." A key goal is to divide refinery operations into fire zones that can be isolated and safely shut down, so that in the event of a fire, the flow of refined products will not fuel the fire.
The guidelines include many protective measures, such as fire protection to improve the ability of equipment and its supporting structures in the event of a fire. Another key measure is to protect critical operating systems when they are exposed to fire.
The standard requires control valves that shut off flow in the event of a fire, as well as control cables that indicate when to shut off fuel, to protect the refinery and its components. According to the standard, control valves and cables must be able to withstand fire for at least 20 minutes, but in some cases up to 30 minutes.
Cable tray systems for protecting cables from fire include: fireproof cable tray systems certified by suppliers. Standard cable trays completely surrounded by insulating, fire-resistant fiber pads or endothermic pads. Cable trays with calcium silicate insulation boards and calcium silicate sleepers, keeping cables away from the bottom of the tray. Trays with galvanized metal plate outer surfaces coated with mastic or intumescent fireproof materials.
Before installation, it must be based on materials used to provide 30-minute hydrocarbon pool fire protection for grouped cables within conduits or cable trays. (Standard test method for fire testing of electrical system component fire-resistant barrier systems). This method is based on a simulation of the type of fire that may occur in a refinery: reaching 800°C in three minutes, reaching 1000°C to 1150°C in five minutes. The test is conducted according to hydrocarbon pool fire temperature curve conditions (50,000+/-2,500 BTU/ft2hr).
Positive pressure is applied to at least half of the test assemblies. Thermocouples are tapped every six inches on both rails of the cable tray, and every six inches on the bare copper wire in the center of the tray. Cable trays are designed without cables, allowing 0% to 100% cable load. When one "group" reaches an average temperature rise of 120°C or any single thermocouple reaches a temperature rise of 120°C, the system fails.
Options to meet fire protection requirements, there are many options to protect control valves and grouped cables from prolonged fire exposure while maintaining control over equipment operated by cables. Wrapping cable trays and conduits with non-flammable, high-temperature resistant insulation blankets is one option. Fire exposure time is proportional to the thickness of the wrap, and the material is usually weatherproof on site. For example, fire blankets are flexible blankets made of high-temperature fibers, suitable for applications up to 1200°C. The core fibers are made using patented fiber technology that uses low bio-persistence insulation wool, reducing the risk to installers.
The blanket wrap system consists of a single layer of 5cm, suitable for cable trays and conduits up to 30cm in diameter. The lightweight flexible blanket packaging is easy to cut, thereby reducing installation problems in complex designs. The simple wrap design allows simple re-entry for cable modifications. To provide excellent installation handling strength, the insulation material is fully encapsulated with fiberglass reinforced foil and polypropylene facing as standard. Weather and mechanical abuse protection are optional additional features. Compared to composite products or rigid board installations, fire protection systems can significantly save materials and labor. It is also lightweight, eliminating the need for additional support structures and their associated costs.
Calcium silicate board is an inorganic, non-combustible, high-temperature resistant insulation material and is another option. This material can provide some weather resistance and durability in many environments, but it is heavy, and coupled with the cutting and fastening methods required, makes installation relatively difficult. In addition, although the board itself is relatively cheap, the waste generated from cutting and the additional labor required for cutting and fastening make installation costly. It also does not respond well to complex cable tray runs.
Endothermic pads are a third option, which protect structural steel, cable trays and conduit circuits by chemically absorbing thermal energy and preventing heat penetration. This product requires installation of three to five layers, leading to increased weight and material costs, five to ten times higher than insulation or board alternatives. These multi-layer solutions also incur additional labor costs. On the other hand, flexible pad solutions are not as insulating, so they are often used to protect power cables that generate heat. The other options discussed are more suitable for protecting control cables that do not generate significant heat.
The goal of petroleum industry standards is to separate refinery fire zones by sufficient distances so that in the event of a fire, the flow of chemicals, petroleum or natural gas to the affected area can be cut off and the fire prevented from feeding itself. In this case, the cables and valves controlling the shut-off valves must be adequately protected. When deciding on the best option to maintain control over these components, consider any relevant differences in total material costs, labor and installation costs, durability at the specific facility location, and long-term maintenance and replacement costs.
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