Safe storage of fertilizers: the case of ammonium nitrate

It's a non-combustible substance in itself, but it is good oxidant, oxidising agent which makes that you cause other combustible substances to burn, even in the absence of air. In addition, decomposes below melting point, generating fumes can be harmful

But the main risk we can find in its storage or handling, is its explosivity. Ammonium nitrate can detonate mainly if there is one of the following factors: confinement, warming, pollution, or strong shock.

We must remember that, in addition to its use for the production of fertilizer, ammonium nitrate is combined with oil for the manufacture of explosives used in terrorist attacks (Anfo), which gives a very visual idea of the danger of the substance of which we are talking about.

The great precedent that learn: plant AZF, Toulouse (France) in 2001

· Cause: accidental contamination of ammonium nitrate with waste of chlorine, increased by the degree of confinement of the store.

· Damage: crater of 50 metres as a result of the explosion, which was recorded as being equivalent to an earthquake of 3.5 degrees on the Richter scale. All buildings and within a radius of 150 m process equipment were destroyed. There were damage to homes, businesses and public buildings in the vicinity (in total amounting to about 2 billion euros).

· Personal injury: 31 people died and more than 2,400 injured.

In recent years, two royal decrees to regulate warehouses of fertilizer based on ammonium nitrate, as well as establishing the minimum requirements for these facilities are safe have been published in Spain:

1 RD 2016 / 2004, which approves the ITC MIE APQ-08: "Storage of fertilizer with high nitrogen content ammonium nitrate":

Applies to products made of ammonium nitrate to be used as it has more than 28% in mass on ammonium nitrate fertilizer, or what is the same, which has more than 80% ammonium nitrate.

Excluded warehouses in process; non-permanent storage, in transit or in expectation of transit; own use with packaged fertilizer stores (< 5t);="" y="" almacenes="" con="" menos="" de="" 50t="" a="" granel="" o="" 200="" t="" envasado=""> to these warehouses shall apply articles 8,9,10 and 11 of the ITC)

These warehouses must locate to minimum distances calculated by multiplying a few basic values depending on the type of installation of reference by a factor (f) depending on the size of the store

Chapter III of the 2016 RD / 2006 contains the General conditions which must be of the warehouses:

• They must comply with the rules of fire safety
• Projected in a single plant, without basements or cellars
• The floor will not have boards and dressing of tar
• They must have insulation that guarantees that the product is always less than 32 ° C
• The roof will have light structure
• They will be installing lightning rods
• Fertilizer will not never come into contact with the electrical or heating.
• Light sources will be cold and incombustible
• The electrical installation shall comply with IT-BT-029

Chapter IV contains the security measures to take, remarking the importance of:

• Avoid dust generation
• Prevent their mixing with other types of fertilizers
• The height of batteries will be 1 m under eaves, vigas…, at least
• They should be 2.5 metres of corridor between the corridors of bagging material, with access from three sides
• Prohibited to use bare portable lamps
• Prohibited to use heat sources
• Banned smoking and fire (must be suitably marked)
• Welding work will be in clean and isolated nitrate surfaces
• Do not use water, sawdust or organic compounds to clean the floor of the store
• Avoid exposure to sunlight
• Do not block departures
• Have forced ventilation to not exceed the admissible maximum concentrations
• Not permitted handling of product in stores, except for loading and unloading
• Indicate the emergency exits
• Place showers and upcoming lavaojos
• Using EPI: gloves of PVC or rubber; masks against dust inert (P1); and in case of fire or decomposition of product has to use filters of Nox, teams of autonomous respiration and protective clothing

2. Dr 888/2006, which approved the ITC MIE AF-1: 'Storage of fertilizer based on ammonium nitrate, with a content of nitrogen equal to or less than 28% by mass': applicable to all solid products manufactured to be used as fertiliser ammonium nitratecontaining a nitrogen content not exceeding 28% on ammonium nitrate mass.

Excluded warehouses in process; the non-permanent storage, in transit or in expectation of traffic; warehouses for own use with a capacity of not more than 500 tonnes; and stores with less than 5000t in bulk or packaged 8000t (to these stores apply them paragraphs 7,8,9 and 10 of the ITC).

They are minor security requirements demanded for these stores, but the most common (used EPI, prohibition of smoking, incompatibility of substances in the storage,...)

In any case, for all types of warehouses with substances containing ammonium nitrate, it is advised adequate training of the workers in contact with the substance and a strict plan of revisions, to avoid unnecessary accidents.