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The need to protect control cables and control valves from fire is one of the key requirements in refineries and other fireproofing locations. There are several options for this, including fire blanket systems, calcium silicate boards, and flexible mats that absorb heat in the event of a fire. All of the available cable fireproofing solutions offer distinct advantages, and refineries must weigh the pros and cons of each to determine which is appropriate for the application.
The "Code for Fire Protection of Petroleum and Petrochemical Processing Plants," provides guidance for "the selection, application, and maintenance of fireproofing materials designed to limit the extent of fire-related property losses in the petroleum and petrochemical industries." 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 does not contribute to the fire.
The guidelines include a number of protective measures, such as fireproofing to improve the ability of equipment and its supporting structures to survive in the event of a fire. Another key measure is protecting 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 refineries and their 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 that protect cables from fire include: Fire-resistant cable tray systems certified by the supplier. Standard cable trays completely surrounded by insulation, fire-resistant fiber mats or heat-absorbing mats. Cable trays with calcium silicate insulation boards and calcium silicate sleepers to keep cables away from the bottom of the tray. Trays with galvanized metal sheet outer surfaces coated with mastic or intumescent fireproofing materials.
Prior to installation, materials used to provide 30-minute hydrocarbon pool fire protection for grouped cables within conduit or cable tray must be tested according to (Standard Test Method for Fire Testing of Fire-Resistant Barrier Systems for Electrical System Components). This method is based on the simulation of the type of fire that may occur in a refinery: reaching 800°C in three minutes and 1000°C to 1150°C in five minutes. Testing is conducted according to hydrocarbon pool fire temperature curve conditions (50,000+/-2,500BTU/ft2hr).
Positive pressure is applied to at least half of the test assembly. 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. The cable tray is designed without cables and allows for 0% to 100% cable loading. The system fails when a "group" reaches an average temperature rise of 120°C or any individual thermocouple reaches a temperature rise of 120°C.
Options for meeting fire protection requirements There are many options to protect control valves and grouping cables from prolonged fire exposure while maintaining control of the equipment operated by the 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 generally weatherproof in the field. For example, the fire blanket is a flexible blanket made of high temperature fibers suitable for applications up to 1200°C. The core fibers are made with a patented fiber technology that uses low-bio permanent insulation wool, reducing the risk to installers.
The blanket wrap system consists of a single layer of 5cm and is suitable for cable trays and conduits up to 30cm in diameter. The lightweight, flexible blanket wrap is easy to cut, which reduces installation issues in complex designs. The simple wrap design allows for simple re-entry cable modifications. To provide excellent handling strength for installation, the insulation is fully encapsulated with a glass fiber reinforced foil and polypropylene face layer as standard. Weather and mechanical abuse protection are optional extras. The fireproofing system offers significant savings in materials and labor compared to composite products or rigid board installations. It is also lightweight, eliminating the need for additional support structures and their associated costs.
Calcium silicate board, an inorganic, non-combustible, high temperature resistant insulation material, is another option. The material can provide some weather resistance and durability in many environments, but it is heavy, which, combined with the required cutting and fastening methods, makes installation relatively difficult. In addition, while the board itself is relatively inexpensive, the waste generated by cutting and the additional labor required for cutting and fastening make installation expensive. It also does not respond well to complex cable tray runs.
Heat-absorbing mats are a third option that protect structural steel, cable trays, and conduit circuits by chemically absorbing heat energy and preventing heat penetration. The product requires installation in three to five layers, resulting in increased weight and material costs that are five to ten times higher than insulation or sheet alternatives. These multi-layer solutions also incur additional labor expenses. Flexible mat solutions, on the other hand, are not as insulating, so they are often used to protect power cables, which generate heat. The other options discussed are better suited for protecting control cables, which do not generate a lot of heat.
The goal of oil industry standards is to separate fire zones in a refinery by enough distance so that in the event of a fire, the flow of chemicals, oil, or gas to the affected area can be shut off and the fire prevented from growing on its own. In this case, the cables and valves that control the shutoff valves must be adequately protected. When deciding on the best option to maintain control of these components, consider the total material cost, labor and installation costs, durability for a specific facility location, and any associated differences in long-term maintenance and replacement costs.
