Case Study | 12.19.2017
Safe Storage and Explosion Control for Hazardous Materials
Design Codes and Criteria
Damage Limiting Construction
Protection Engineering Consultants (PEC) and its principals and engineers are known for decades of experience related to threats and hazards from the detonation of high explosives and improvised explosives, and, for design expertise in mitigating the effects of these explosions. Our engineers are also known for their structural and architectural designs to resist the effects of accidental fuel-air explosions such as those at petrochemical plants where siting studies have been performed to identify risks and hazards in the form of prescribed dispersion, fuel reaction and resulting peak pressures and impulses.
More recently, engineers at PEC, are building strong resume of projects for a larger range of industries that are concerned with hazardous and energetic materials. These industries process and use hazardous materials as feedstock in the chemical, food and agricultural, construction materials, fuels and lubricants, paints and inks, and electronics (microprocessor and battery technologies) fields. The probability of occurrence of accidental releases and unwanted reactions in these process and manufacturing industries is considerably greater than that of the anti-terrorism and force protection fields, and these industries require robust and cost-effective means of managing the resulting risk. Because of the risks, national and international code authoring and code maintenance bodies and councils, such as the International Code Council (ICC), have generated codes and standards (International Building Code (IBC), International Fire Code (IFC)) that include requirements for hazardous materials handling, which are accepted and codified in law, in part or in full, by municipalities around the US. These codes and standards are undergirded by supporting practice standards produced through research and experience derived from user community committees in organizations and associations such as the National Fire Protection Association (NFPA).
Ultimately, industry and their customers benefit from safe and efficient operation of their plants and production facilities. Unfortunately, the numerous codes, practice standards, local modifications to those standards, and the complexity inherent in defining the makeup of chemicals and dusts that can be hazardous, makes it difficult to determine what structures and storage configurations are both safe and optimal. In the last few years, PEC has developed expertise and a robust understanding of the requirements and standards to help our clients navigate the regulatory and practice approaches. We’ve assisted in designs for bakeries, ink plants, chemical purification processes, fiberglass manufacturing, composites forming, and fuels and lubricants test facilities.
In these projects, the materials delivered, handled, stored, pumped, combined, mechanically altered and otherwise used in a manufacturing, baking, agricultural or specialty production process, are generally considered first. We help the customer understand the requirements of the IBC in determining hazardous area classifications, and, based on the chemical formulations and physical makeup of the materials, we help them define the flammability, combustibility or water reactivity hazards. These definitions and the storage and process operations or handling of the materials (closed storage, closed system use or open use) can then define Maximum Allowable Quantities per Control Areas from Chapter 20 of the IFC entitled “Hazardous Materials – General Requirements”, Section 5003 and Table 5003.1.1 (1) of the IFC. In general, when maximum allowable quantities are not exceeded, no special provisions for explosion control (means of controlling a potential deflagration reaction) are required; only the special requirements for control areas and control areas with fire suppression apply. Table 5003.1.1 (1) lists quantities for a variety of hazardous materials including combustible dusts, combustible fibers, combustible liquids, consumer fireworks, cryogenic materials, flammable gases, flammable liquids, flammable solids, peroxides, oxidizers, pyrophorics, unstable reactive and water reactive materials. Many of these categories have subset classifications, where chemical and physical properties are used to classify those materials. For example, combustible (II, IIIA and IIIB) and flammable (IA, IB and IC) liquids are classified by flash point and boiling point, indications of likelihood of flammable or combustible vapor formation during use or in the event of spills in storage areas. Likewise, and as another example, water reactive materials (Classes 1, 2 and 3) are classified according to laboratory determined heat of mixing (heat energy released during mixing and reaction). Quicklime, or Calcium Oxide (CaO) is a water reactive material used by the 100’s of tons in construction material fabrication. While quicklime itself is not flammable or combustible, and doesn’t release mechanical energy in the form of pressure when reacted with water, it does release enough heat when reacted with water to cause nearby flammable materials to ignite; hence it is designated as a Class 2 water reactive material.
When materials are stored in quantities in excess of those listed in the IFC’s Table 5003.1.1 (1), as they often are, certain materials or combinations of materials will require explosion barricading or the use of methods for explosion control. Table 911.1 of the IFC dictates these requirements for combustible dusts, cryogenic gases, explosives (non-detonable), flammable gases, flammable liquids, pyrophorics, and reactive and water reactive materials. The table also includes a caveat or “catch-all” that states that explosion control is also required in “…Rooms containing dispensing and use of hazardous materials where an explosive environment can occur because of the characteristics or nature of the hazardous materials or as a result of the dispensing or use process.” Explosion here has a specific meaning, in that it refers to reactions other than detonations producing shocks, since the methods for explosion control work in regimes where flame front velocities are slow enough to allow mechanical systems to open and vent, thereby limiting the maximum pressure experienced by the room structure.
The requirements for explosion control can be achieved through a variety of means as facilitated by supporting NFPA documents such as NFPA 68, “Standard on Explosion Protection by Deflagration Venting” and NFPA 69, “Standard on Explosion Prevention Systems.” NFPA 68 provides methods for determining vent opening sizes and construction requirements or mechanical vent operating parameters as a function of hazardous material properties, storage volume, containment room geometry and structure strength, available fuel and oxygen (stoichiometry), and internal obstructions (flame accelerating) surfaces. NFPA 69 provides approaches and requirements to eliminate the explosion venting requirements through the use of instrumentation and sampling that supports the activation of supplemental ventilation systems designed to keep fuel-air concentrations at a fraction of the stoichiometric mix for the stored materials. This approach often is the most robust and safest where open-use hand addition and hand mixing of chemicals is done and where local concentrations of flammable vapors can greatly exceed average concentrations in the overall room volume.
Numerous parallel requirements exist when hazardous materials are present. NFPA 30, “Flammable and Combustible Liquids Code” includes electrical requirements (NEC class and division) based on chemical hazard class. The IFC and NFPA 400 “Hazardous Materials Code” include spill control and secondary containment requirements for hazardous materials. NFPA 55, “Compressed Gases and Cryogenic Fluids Code,” NFPA 62, “Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities,” NFPA 67, “Guide on Explosion Protection for Gaseous Mixtures in Pipe Systems,” NFPA 91, “Standard for Exhaust Systems for Air Conveying of Vapors, Gases, Mists and Particulate Solids,” NFPA 484, “Standard for Combustible Metals,” and other supporting documents all include special requirements as their titles indicate.
At PEC, our background in energetic and hazardous materials, the physics of their often violent reactions and the response of structural systems to these reactions gives us significant insight into the interpretation of the methods and requirements of this seemingly complex and endless list of codes and standards. Call or email us with your particular industrial project design challenges related to hazardous materials storage and use. We would be delighted to assist.