As part of the response to President Obama’s Executive Order to review safety rules at chemical facilities, an inter-agency chemical advisory has been issued from OSHA, EPA and ATF regarding the handling, storing, and emergency response to ammonium nitrate. Ammonium nitrate, as you recall, was one of the major factors that resulted in the deadly explosion at the West Texas fertilizer plant in April. I wrote about that here, and talked briefly about the President’s Executive Order here.
You can read the advisory here, but I’d like to describe some of the main points that could have been key factors in the recent disaster in Texas:
One of the major things to consider about the storage of ammonium nitrate is that the substance will self-confine under certain conditions. To take the example of the explosion of the SS Grandcamp and the SS High Flyer back in 1947, the many tons of ammonium nitrate stored on those vessels were heated in confined spaces, and when the captain of the SS Grandcamp ordered his crew to pump steam into the hold in order to smother the fire, the ammonium nitrate was heated, confined, and under pressure.
Believe it or not, one of the standard methods for breaking up ammonium nitrate that had caked itself into large chunks was to use explosives! This method led to several larger unintended explosions on a few occasions. This method is no longer used. And organic packing materials, such as wax-coated paper, are no longer used to package ammonium nitrate (this material, if burned, provides fuel for an explosion).
Because of this, facilities that stock or store ammonium nitrate should take care that it is not co-located with materials that readily burn, like grain, sugar, seeds, sawdust, and petroleum fuels.
Bulk storage of ammonium nitrate should be carefully managed. As you can read in the chemical advisory, the material should not be stacked or storage directly against walls or ceilings, requiring 30 inches of clearance from walls and 36 inches of clearance from the ceiling. Aisles between stacks of ammonium nitrate should be at least 36 inches wide, and those stacks should not exceed 20 feet high, 20 feet wide, and 50 feet long.
Fire Protection and Emergency Response
Storage areas containing ammonium nitrate should be equipped with an automated fire sprinkler system, or at least an automatic fire detection system. However, if the amount of material stored exceeds 2,500 tons, a fire sprinkler system is required. Facility owners should ensure that the appropriate types of fire extinguishers should be readily available (not all types of fire extinguishers are recommended for ammonium nitrate).
Local fire emergency services should visit facilities that contain ammonium nitrate and formulate emergency response plans specifically for emergencies involving ammonium nitrate. Storage conditions and material handling should be reviewed as well, and the emergency plan should take into account not only the facility, but the surrounding structures (businesses, schools, homes, etc.).
The chemical advisory specifically states that facilities that use and/or store ammonium nitrate have a responsibility to their surrounding communities that the local first responders have the appropriate response plans in place.
Guidelines for fire fighters responding to a fire involving ammonium nitrate should evaluate the conditions to determine their actions. They should not fight the fire if:
- The fire involves ammonium nitrate and is judged to be out of control
- The fire is engulfing the ammonium nitrate
- Brown or orange smoke is visible, which indicates the presence of nitrogen dioxide, a toxic gas that forms when ammonium nitrate decomposes
- There is a rapid increase in the amount or intensity of smoke or fire in an ammonium nitrate storage area
In these cases, the fire fighters should abandon all fire-fighting attempts and remove themselves from the immediate vicinity, focusing on any evacuation efforts that might become necessary.
If a fire involving ammonium nitrate is considered to be under control enough to attempt fighting, the fire fighters should:
- Fight the fire from protected locations or the maximum effective distance. They should approach it from upwind to avoid any possible toxic fumes that may result from decomposition of the material. They should use SCBA as a means of protection against harmful fumes and gases.
- Use flooding quantities of water from a safe distance as soon as possible. The ammonium nitrate must be kept cool and the fire should be extinguished quickly. Unmanned hose holders or monitor nozzles should be used if possible.
- NOT use steam, CO2 or foam/dry extinguishers, or any kind of smothering agents (this may cause the material to self-confine).
- Prevent as much as possible the run-off from the extinguishing water from entering municipal drains, so as to minimize environmental impact.