New Developments in Explosion Protection Technology

New developments in explosion protection technology during the last five-toten years include: new explosion prevention and suppression systems using either reticulated foam inserts, fine water mist, or onboard oxygen concentration reduction; explosion isolation systems; flameless deflagration venting devices; and new products and methods for design, construction and analysis of blast resistant structures. Key features of these new developments, and the corresponding explosion protection standards that provide guidance on their use, are summarized in this paper. Many of the developments and applications are pertinent to industrial facilities processing or storing large quantities of flammable gases, vapors, or combustible powders. Other applications include military and commercial aircraft, tanker trucks and rail cars, ship fuel tanks, and portable containers for flammable liquids. Blast resistant structure technology has the most diverse applications, encompassing blast and projectile resistant walls and buildings. Introduction Several international events and trends in the last five to ten years have stimulated the development of new explosion protection technology. These include: 1) more regional and international explosion protection standards, 2) some widely reported tragic commercial airline explosions, 3) government agencies investigating and reporting on destructive/fatal industrial explosions, 4) increased competition among manufacturers and providers of explosion protection systems, and 5) realization that terrorism represents a more widespread explosion threat to many buildings and structures. As a result, there are now new methods, devices, and systems to accomplish inerting of fuel tanks and flammable liquid storage tanks, improved and more flexible design guidance and hardware for deflagration venting, new active and passive explosion suppression systems for vehicle/aircraft fuel tanks and industrial equipment, a variety of explosion isolation systems to prevent propagation of gas and dust explosions between process equipment, and many new blast resistance and mitigation products for use on high risk buildings and structures. New developments in each of these explosion protection areas are summarized here. New Inerting Technology Explosion prevention via inerting requires that the oxygen concentration be reduced below the Limiting Oxygen Concentration (LOC) for a particular fuel at a specified temperature and pressure. The LOC is the smallest concentration of oxygen that can support flame propagation at the stated temperature and pressure. LOC values for many flammable gases and combustible dusts are listed in the Appendix of NFPA 69 [1]. Most of the values are in the range 9 – 12 percent by volume for nitrogen inerting, and are about 3 vol% higher for carbon dioxide inerting. In cases without any published data, Britton [2] recommends that the following equation can be used to estimate the LOC for nitrogen inerting. 2 c S H / Const LOC ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ∆ = [1] where ∆Hc is the material’s net heat of combustion in units of kcal/mole fuel, S is the stoichiometric oxygen/fuel ratio, and Const = 9.22x10 for hydrocarbons, and = 1.032x10 for fuels with C, H, O, N compositions. For example, propylene has a ∆Hc of 460 kcal/mole and an