oct 29, 2020

Do you know how to protect your industrial structures against fire?

  • Artículo
  • industrial
  • structures
  • protection
  • steel
  • ANSI/UL 1709
  • CAN/ULC‑S101

Why protect steel from fire when it doesn’t burn? This is a frequently asked question, despite the well-known fact that steel is a fireproof material. Under load, steel, a great heat conductor, begins to lose its design safety margin at temperatures above 300°C, and its strength decreases as its deformation increases. Excessive deformation can cause steel to collapse and compromise compartmentalization and integrity.

  1. It is therefore crucial that a passive fire protection system delay the rise in temperature to preserve the building’s stability and allow occupants to leave the building and firefighters to enter and extinguish the fire.

    When a fire breaks out in an industrial facility, steel needs to retain its structural integrity long enough to allow workers to evacuate safely and to prevent primary structures from collapsing. The goal is to mitigate damage to adjacent equipment requiring a minimal delay before the plant can be restarted after a fire.

    Guidelines for the fire protection design of buildings are published in the 2010 National Building Code of Canada (Division B, Part 3). The Code cites the Underwriters’ Laboratories of Canada (ULC) standard, CAN/ULC‑S101, “Standard Methods of Fire Endurance Tests of Building Construction and Materials”. During these tests, structures are subjected to a standard time‑temperature curve that rises to 840°C in 30 minutes. This scenario represents a cellulosic (dry) fire that can occur in residential and commercial buildings.

    However, a fire occurring in an industrial complex is likely to be much stronger. There are three main classes of fire: gas fires (natural gas, butane, propane or other gaseous products), grease fires (hydrocarbons, tar, fats, oils, paints, varnishes, alcohols, solvents and other chemicals) and metal fires, where temperatures will reach 1,000°C in mere minutes.

    Since the ULC‑S101 code does not cover this type of fire, for industrial projects it is important that an engineer specializing in health, safety and environment (HSE) be involved from the outset. The engineer participates in HSE hazard identification (HAZID) activities and develops specifications that include HSE standards and regulations. Depending on the type of industry, the engineer also identifies fire classification, determines fire scenario envelope dimensions, evaluates the fire-resistance rating and specifies the durability of the protective coating to be applied on the installations (equipment, piping or structures) identified as fire hazardous.

    Based on these specifications, the structural engineer designs the fireproofing for the structures. Materials must be chosen based on constructibility, i.e. whether the coating will be applied to members in the plant or on site, whether the fireproofed structure will be modular, installed on site or lifted with a crane and placed in its permanent position.

    It is the structural engineer who must control the load transfer hierarchy to determine the main members to be fireproofed. This engineer must also select the steel grade, stress level, profile type, bound and load condition, as well as the massivity factor (ratio between the heated surface area and the volume of the area). “Heavy” steel requires less fire protection than “lighter” steel. Generally speaking, the “heaviness” of steel is determined by the ratio between its perimeter exposed to fire and its cross-sectional area. The higher the ratio, the higher the degree of fire resistance required.

    In the petrochemical, oil and gas industry, standard ANSI/UL 1709, “Standard for Safety Rapid Rise Fire Tests of Protection Materials for Structural Steel”, is often used. These tests evaluate the performance of a material in a furnace able to reach 1,103°C in five minutes of operation. The materials must provide enough fire protection for the equipment to maintain its structural integrity for 30 minutes in a fire at 1,093°C. The standard defines, among other things, the minimum thickness of a fire-retardant coating to be applied based on the required fire-resistance rating.

    The structural engineer must therefore specify the thickness and type of fireproofing coating for structures supporting critical equipment. The coating could be a cementitious product or an intumescent paint.

    A wide range of fire-retardant materials are available on the market. You can rely on BBA’s structural engineers to help you learn how to use these products and on what structural elements they should be applied. These professionals have solid expertise in fireproofing industrial structures and can assist you with the design and preparation of technical specifications and drawings with standard details, based on your needs and your facilities’ requirements.

This content is for general information purposes only. All rights reserved ©BBA

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