Fertile Soil for Safety: OSHA’s Ammonium Nitrate Storage Rules

The earliest recorded disaster involving ammonium nitrate (AN) occurred on April 16, 1947, in Texas City, Texas. A transport vessel loaded with 2,600 tons of AN caught fire; when the fire spread to the sealed storage hold, the transport exploded, killing 581 people—including all but one member of the Texas City Fire Department.

We’ve known for a long time that AN has disastrous potential. If you store more than 1,000 pounds or more of AN on your site, the rules below apply.

Safe Storage Rules

OSHA’s rules for AN storage are found in 29 CFR 1910.109(i), and apply to most commercial forms of AN. The rules, which are very detailed, cover:

Building construction. AN must be stored in buildings and storage areas that:

• Are a single-story, no more than 40 feet tall


• Have no basement


• Have noncombustible, solid flooring


• Are dry and well-ventilated


• Have corrosion-resistant wiring and (where needed) lightning protection


• Are of fire-resistant construction, if exterior walls are within 50 feet of any combustible structure, vegetation, or storage area


• Are secured against unauthorized entry


• Are clearly marked with signs reading “Ammonium Nitrate” in 2-inch letters

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Fire protection. To prevent fires and explosions:

• Refuse containers or shipments of AN with temperatures exceeding 130ºF.


• Leave at least 30 inches between stored AN and building walls and partitions, and leave 3-foot aisles between piles, with at least one 4-foot main aisle.


• Install automatic sprinkler systems where more than 2,500 tons of AN are stored.


• Provide water, hoses, and fire extinguishers as needed.

Bulk storage to prevent contamination. To prevent contamination of AN:

• Keep bins clean and free of potential contaminants.


• Avoid galvanized iron, copper, lead, and zinc in bin construction. Aluminum bins and wooden bins protected against impregnation by AN are permissible.


• Separate AN from potential contaminants using impregnable partitions or at least 30 feet of open space.


• Do not store flammable liquids (gasoline, kerosene, solvents, and light fuel oils), LP-gas, sulfur and finely divided metals, explosives or blasting agents, or any other flammables or combustibles in the same building with AN.

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Storage to prevent fires from impacting piles of AN. Compacted AN is very dangerous. To prevent compaction:

• Limit pile heights to 20 feet, and footprints to 20 feet by 50 feet.


• Do not pile or stack AN closer than 36 inches below the roof or supporting beams.


• To minimize caking, ensure that inventories are managed so that all AN is moved out periodically.

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