Monday, October 7, 2013

Ammonium Nitrate (AN): Safe Storage, Handling, & Management Part 2

What steps should facility owners or operators take to reduce the hazards of AN during storage and handling?
Storage/Process Conditions to Avoid
Persons engaged in the handling, management or emergency planning for AN must be aware of the hazards of AN and ensure that the conditions that may lead to an explosion are not present. Measures that facilities should take to ensure the safe storage, use and handling of AN include:
  • Avoid heating AN in a confined space.
    • Processes involving AN should be designed to avoid this possibility.
    • Avoid localized heating of AN, potentially leading to development of high temperature areas (e.g., AN fertilizer should not be stored near sources of heat such as steam pipes, radiators, hot ducts, light bulbs etc.).
  • Ensure that AN is not exposed to strong shock waves from explosives. AN storage near high explosives or blasting agents must conform to ATF's Table of Separation Distances, Title 22 of the Code of Federal Regulations, section 555.220 (22 CFR 555.220).
  • Avoid contamination of AN with combustible materials or organic substances such as packing materials, dust, seed, oils, and waxes.
    • If possible, do not co-locate AN, especially bulk AN in bins, with dust-producing organics such as grains or seeds.
  • Avoid contamination of AN with inorganic materials that may contribute to its sensitivity to explosion, including chlorides and some metals, such as aluminum powder, chromium, copper, cobalt, and nickel.
    • Pay attention to the materials used to build storage areas and cribs. Wood and aluminum or other metals must be specially treated to prevent impregnation if they are going to be in contact with AN. Metal materials can be treated with epoxy tar or chlorinated rubbers to prevent corrosion of the metal and contamination of the AN.
  • Maintain the pH of AN solutions within the safe operating range of the process. In particular, avoid low pH (acidic) conditions.
    • If possible, do not co-locate acids in an AN storage area.
  • Keep molten or solid AN out of confined spaces, especially sewers or drains where it can react with organic materials there.
Certain specific safety and handling instructions (required and recommended) apply for safe handling and storage of AN6 under certain conditions:

OSHA's standard for Explosives and Blasting Agents at 29 CFR 1910.109(i) contains requirements for AN stored in the form of crystals, flakes, grains or prills including fertilizer grade, dynamite grade, nitrous oxide grade, technical grade, and other mixtures containing 60 percent or more of AN by weight. AN should also be handled in accordance with safe practices found in NFPA 400 Hazardous Materials Code, Chapter 11.
Building Design
  • Store only in one-story buildings and buildings with no basements, unless the basement is open on one side.
  • Use fire resistant walls within 50 feet of combustible building or materials.
  • Flooring in storage and handling areas should be constructed of noncombustible material or protected from impregnation by AN.
  • Avoid installing, or remove or close off any open drains, traps, tunnels, pits or pockets into which molten AN can flow and be confined in the event of fire.
  • Buildings should be kept dry and free of water seepage through roofs, walls and floors.
  • Have adequate ventilation or be constructed to self-ventilate in the event of a fire to avoid pressurization.
  • Do not place AN into storage when the temperature of the product exceeds 130°F (54.4°C).
Storage in bags, drums or other containers
  • Piles of bags, drums and other containers should be no closer than 36 inches below the roof or supporting beams.
  • Bags should be stored no less than 30 inches from walls or partitions.
  • Piles of bags, drums, and other containers should not exceed a height of 20 feet, width of 20 feet, and length of 50 feet, unless the building is of noncombustible construction or protected by automatic sprinklers.
  • Maintain aisles of at least 3 feet width between piles.
Storage in bulk
Bins for storing bulk AN should be kept clean and free of materials, which could contaminate the material. Bins should not be constructed of galvanized iron, copper, lead or zinc unless suitably protected. Aluminum or wooden bins should be protected against impregnation by AN.

  • Piles or bins must be adequately sized, arranged and moved periodically to minimize caking. Height or depth of piles shall be limited by pressure-setting tendency of the product, but in no case should pile be higher than 36 inches below roof or supporting beams.
  • Do NOT use dynamite, explosives or blasting agents to break up or loosen caked AN.
  • Protect piles of AN from absorbing moisture from humid air by covering them with water-impermeable sheeting or using air conditioning.
  • Do not store AN with organic chemicals, acids, or other corrosive materials, materials that may require blasting during processing or handling, compressed flammable gases, flammable and combustible materials or other contaminating substances. AN stores should be separated from incompatible substances by using separate buildings or 1 – hour fire resistant walls, or a minimum separation distance of 30 feet.
Fire Protection
  • AN storage areas should be equipped with an automatic sprinkler system, or have an automatic fire detection and alarm system if the areas are not continuously occupied. This is especially important when the facility in question is close to the public surrounding the facility.
  • Facilities should NOT store more than 2500 tons of bagged AN without an automatic sprinkler system.
  • An automatic sprinkler system, if installed, should be provided in accordance with NFPA 13, Standard for the Installation of Sprinkler Systems.
  • Suitable fire control devices such as hoses and appropriate portable fire extinguishers (AN is an oxidizer and not all fire extinguishers are appropriate) shall be provided throughout the warehouse and loading areas. Water supplies and fire hydrants should be available.
  • Store AN fertilizer in separate buildings or separated by approved fire walls from organic, combustible or reactive materials, such as grains, wood or other organic materials, urea and urea compounds, flammable liquids or gases, corrosive acids, chlorates, chromates nitrites, permanganates or finely divided metals or sulfur.

  • AN fertilizer should NOT be stored in the same building with explosives or blasting agents unless conditions in ATF's Table of Separation Distances of Ammonium Nitrate and Blasting Agents from Explosives and Blasting Agents, 27 CFR 555.220, are met.
  • Prohibit smoking in AN storage areas.

  • We recommend that AN be stored in purpose-built facilities/buildings of non-combustible construction. Dust-producing organic materials, such as grain, seeds and sugar, should not be stored near AN. Some metal powders such as aluminum powder are equally dangerous. AN should be stored so as to ensure it is not contaminated by gasoline, diesel or other fuels, and is not subject to high heat (even in one small area of a large stockpile) or water infiltration.

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