Lessons learnt from Ammonium Nitrate explosions and the way ahead

There have been a number of disasters due to ammonium nitrate explosions and the recent ammonium nitrate-fueled explosion in Beirut was one of the largest accidental explosions.  The focus is on how 2,750 tons of Ammonium nitrate, a highly explosive chemical used in fertilizers, seem to be stored in a ware house for six years without proper safety controls. It has been reported that the warehouse held illegal stores of ammonium nitrate, which caught fire and caused a series of blasts. This almost certainly has contributed to the tragic circumstances that resulted in a fire causing such a devastating explosion. In all explosions there is a rapid conversion of the explosive material into a large volume of hot, high pressure gas, the sudden release of which results in a so -called blast wave which radiates from the source in all directions. This recent Beirut explosion can be considered as a ‘high order’ explosion, with an obvious blast wave seen to be propagated from a massive secondary explosion, that followed on from the event. The safety challenges associated with ammonium nitrate coupled with poor safety management culture could largely be considered as the most important contributing factors for the accident.

All about Explosion and Explosives

Explosives are categorized as high order explosives or low order explosives.

• High order explosives have a strong supersonic pressure wave, known as the blast wave or shock wave.
• Low order explosions have a subsonic explosion and lack the high order explosive blast wave. Examples of low order explosives include – pipe bombs, gun powder, petroleum-based bombs.

In addition to the blast wave, an explosion can cause blast wind. Blast wind is the flow of superheated air that can interact with people and objects and cause injury or damage.

Chemical explosions cause injuries in four categories (primary, secondary, tertiary, and quaternary). The four categories are based on the impact on the human body due to the blast wave, blast wind, environmental/material factors present in the area of the blast.

Immediate death can occur from an explosion as a result of extensive pulmonary injury with pulmonary hemorrhage causing suffocation. Immediate death can also be caused by a pulmonary air embolism, severe head injury, significant internal injuries.

Why is the Ammonium Nitrate so dangerous?

Ammonium nitrate was first produced in 1659. It is a “dualuse” substance from which either fertilizers or explosives can be produced. It is produced at a large scale throughout the world. Ammonium nitrate (AN) primarily is used as a fertilizer but it is also very important compound in the production of industrial explosives. Millions of tons of ammonium nitrate are produced annually throughout the world. Although ammonium nitrate generally is used safely, accidental explosions involving AN have high impact resulting in loss of lives and destruction of property.

Ammonium nitrate is a stable compound and generally is difficult to explode when it is in solid or molten form or in solution. However, ammonium nitrate may explode when it is exposed to strong shock or to high temperature under confinement. The presence of certain contaminants may increase the explosion hazard of ammonium nitrate.

Ammonium nitrate by itself does not burn, but in contact with other combustible materials, it increases the fire hazard. It can support and intensify a fire even in the absence of air. Fires involving ammonium nitrate can release toxic nitrogen oxides and ammonia. A fire involving ammonium nitrate in an enclosed space could lead to an explosion.

In a large quantity of ammonium nitrate, localized areas of high temperature may be sufficiently confined by the total quantity to initiate an explosion. The explosion of a small quantity of ammonium nitrate in a confined space may initiate the explosion of larger quantities.

THE MAIN CHEMICAL HAZARDS ASSOCIATED WITH AMMONIUM NITRATE:

The main chemical hazards associated with ammonium nitrate are Fire, Decomposition and Explosion.

Ammonium nitrate decomposes, non-explosively, into the gases nitrogen oxides and water vapour when heated. However, it can be induced to decompose explosively by detonation.

Large stockpiles of the material can also be a major fire risk due to their supporting oxidation, a situation which can easily escalate to detonation. Ammonium nitrate can explode through two mechanisms:

• Shock-to-detonation transition. An explosive charge within or in contact with a mass of ammonium nitrate causes the ammonium nitrate to detonate.
• Deflagration to Detonation Transition The ammonium nitrate explosion results from a fire that spreads into the ammonium nitrate (Recent Beirut explosion), or from ammonium nitrate mixing with a combustible material during the fire (Repauno, Cherokee, Nadadores).

Lessons learnt from Ammonium nitrate explosions

Finally, lessons learned from past major accidents that have occurred around the world could be beneficial for operators to recognize gaps in the safety management system and improve the safety performance by implementing all necessary safety protocols.

• Ensuring the regulatory analysis for compliance with federal, state and local regulations.
• Facility siting and land use planning implications and ensuring that ammonium nitrate is stored securely and in accordance with local regulations.
• Ammonium nitrate must be stored in a cool, dry, well ventilated place, out of direct sunlight and separate from combustible, organic or other readily oxidizable material. If ammonium nitrate is to be stored in bulk, the surface must be treated so that it is resistant to attack and penetration. Bulk ammonium nitrate should not be stored on a bituminous floor. Concrete floors are recommended for storage. Areas of possible confinement should be eliminated to prevent entrapment of material or eventual molten ammonium nitrate to flow during a fire.
• Storage areas should be inspected regularly by an individual trained to identify potential hazards and ensure that all safety and security control measures are being properly implemented.
• Ammonium nitrate must be avoided contamination with combustible or flammable materials, strong acids, strong bases, strong oxidizing agents, reducing agents, chlorinated compounds (chlorates, chlorides), permanganates, peroxides, metal powders and copper and any copper-alloys like bronze and brass.
• Need for local coordination of risk information and emergency planning.The personnel must be trained in the prevention of risks, the detection of abnormalities and in emergency response associated with ammonium nitrate.
• A sound characterization of the risks involved, particularly involving an understanding of dangerous materials implicated is indispensable for implementing efficient fire prevention and fire-fighting plans.
• It is essential that each emergency centre should hold an inventory of potential risks for its sector of intervention to enable efficient response.
• Effective response requires also that there should be adequate and permanently available sources of water including, for example, when the tide is going out.
• Facilities should be appropriately constructed and maintained to avoid leaks, flooding, or formation of pockets of moisture in areas where the ammonium nitrate is located.
• Employees should be regularly trained and tested on critical safety procedures and periodic monitoring should take place to ensure that procedures have been followed.
• Furthermore, authorities are responsible for intervening to address land-use planning concerns around ammonium nitrate installations.
• Ensure that adequate safety procedures in particular relating to training and awareness of hazards are imparted.

Legal aspects in India about Ammonium nitrate

Ammonium nitrate (AN) has drawn increased attention from authorities over the last years because of various accidents. Relevant safety, health and environmental regulations and security issues are related to the safety of manufacture, handling, storage and transportation of ammonium nitrate.

 The manufacture, conversion, bagging, import, export, transport, possession for sale or use of ammonium nitrate is covered under The Ammonium 

Nitrate Rules, 2012. The rules also make storage of ammonium nitrate in large quantities in populated areas illegal in India.

For the manufacture of ammonium nitrate, an Industrial licence is required under the Industrial Development and Regulation Act, 1951. A license under the Ammonium Nitrate Rules, 2012 is also required for any activity related to ammonium nitrate.

Article by Dr.Yashoda Tammineni,

MSc, Ph.D.

HSE, HOD at NIFS