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expert reaction to Beirut explosion

A large explosion in Beirut, Lebanon, was reportedly caused by a large quantity of ammonium nitrate stored in a warehouse near the port. 


Commenting on whether there will likely be remaining health impacts of exposure:

Prof Andrea Sella, Professor of Inorganic Chemistry, UCL, said:

“I don’t think there is any significant hazard.  It is not volatile (i.e. it doesn’t fly) and as most of the ammonium nitrate will have gone and the remainder can be washed away into the sea where it will fertilise things.

“The NO2 in the plume is clearly toxic but will have been projected high above the city and will gradually disperse in the wind.  Unlikely to be locally toxic.”


Comments on the explosion itself:

Prof Jacqueline Akhavan, Head of Centre for Defence Chemistry, Cranfield Defence and Security, Cranfield University, said:

Is it explosive – why might this have happened?

“No, it is not classed as an explosive when it is stored correctly in bales of less than 1m3.  However if it is stored in a large pile, above its critical diameter and initiated, it can have explosive properties.

Is there anything that you can tell from the footage of the explosion?

“It is my understanding that there was a fire which initiated fireworks.  This fire then spread to the ammonium nitrate pile which started to burn giving off NOx products, water as a gas and nitrogen.  As the ammonium nitrate burnt the gaseous products within the pile could not escape causing the burn rate to increase.  When the speed of the burn became supersonic (greater than the speed of sound through the material) the ammonium nitrate detonated resulting in a supersonic shock travelling through the material which became a blast wave when it travelled through the atmosphere.  The blast wave would contain pressures of GPa (Giga Pascals) and temperatures over 3000oC.  The blast wave can travel great distances causing damage to buildings, cars, people etc.

Is there anything that you can tell from the extent of the damage and how away the blast was felt?

“If you are close to the blast wave it would lift you off the ground and throw you in the direction of the blast wave.  The pressures would cause damage to the ear drums, lungs, organs, and result in broken bones.  The high temperatures would result in burns to the skin and lungs.

Any other comments?

“The initiation of ammonium nitrate must be through a fire.  Ammonium nitrate absorbs water and becomes over a period of time, a hard solid rather than a powder.  The velocity of detonation increase with density so the power of the explosion is greater in a solid compared to a powder.”


Prof Geoffrey Maitland CBE FREng FIChemE, Professor of Energy Engineering, Department of Chemical Engineering, Imperial College London, said:

What is ammonium nitrate?

“Ammonium Nitrate is a salt which takes the form of a white crystalline solid, not too different in appearance from common table salt (sodium chloride).  It is found naturally but is made in large quantities by reacting the gas ammonia with nitric acid.  In itself it is quite innocuous, being non-poisonous like sodium chloride and stored properly (in water-tight containers) is relatively stable.  Its main applications are as a fertiliser and as a component in explosives used, for instance, in mining.

Is it explosive – why might this have happened?

“If kept isolated and unconfined, it is quite stable.  If in an open space where the heat can escape, if heated it decomposes to oxides of nitrogen (which are a health hazard) and water vapour but will not catch fire.  However, if it comes into contact with an intense source of heat and ignition, such as a detonator or an intense fire for some time, and is present as a large bulk mass (e.g. confined within containers or sacks, which may themselves be flammable) and in a confined space, such as a warehouse, then it can explode.  It decomposes rapidly to gases, because of the confinement heat cannot escape, the gases rapidly expand and the explosion occurs.  This releases an enormous amount of energy, and sends out a shock wave as the surrounding air is rapidly compressed which propagates very rapidly over the surrounding area and does enormous damage to buildings and people.  This is what seems to have happened in Beirut yesterday.

Is there anything that you can tell from the footage of the explosion?

“From the footage there was initially a large cloud of what looks like white/grey smoke from behind the white building which may be the storage warehouse.  So this indicates that there may have been a fire close to or even inside the store, which was  probably the source of heat (and maybe of ignition for flammable packaging) which set off the explosion of the 2750 tonnes of ammonium nitrate reportedly stored there.  When the explosion happened, a new mushroom shaped cloud rapidly developed and expanded rapidly over a wide area, inland over the port and out over the water.  This has an orange, red/brown colour which is characteristic of nitrogen dioxide, one of the decomposition products of ammonium nitrate, which is a very good indicator that this substance was involved and the likely source of the explosion.  The mushroom type cloud is formed by the rapidly expanding gases which rise upwards as they are heated and so have a lower density than the surrounding air.  They rise in the stem of the mushroom and then because they are rising very quickly give rise to turbulent instabilities inside the cloud which give recirculating air/gas regions at the top which cause the cloud to balloon out and have its characteristic mushroom shape.  The pressure shockwave radiates outwards through the air much more quickly and its effects are felt much further away within seconds.  You can see buildings raised to the ground instantly when the pressure wave reaches them.  You can imagine what this will do to any humans in its wake.  They stand little chance of surviving.

Is there anything that you can tell from the extent of the damage and how away the blast was felt?

“Aerial photos and film indicate that the damage spread over several kilometres and there are reports that the blast was felt several hundred kilometres away in e.g. Cyprus.  This just illustrates how much energy was released so rapidly from almost 3000 tonnes of this chemical.  It confirms that a large amount of material must have been involved and that the fire transitioned to a detonation limit to give such a large, rapid explosion.

Any other comments?

“It seems the material had been impounded and then stored for some 6 years or so.  It could be that long-term storage had caused some deterioration of the ammonium nitrate and made it more susceptible to explosion.  For instance, if the storage was not airtight, in the humid conditions of Beirut, the salt could have taken up large quantities of water from the air which would cause the granules and pellets to fuse over time into a large consolidated mass from which heat and gases from the decomposition could not escape as easily as from a dispersed granular, free-flowing pile of fine particles.  This would have just added to the confinement effect which increased the risk of an explosion once a source of heat was applied.

“Ammonium Nitrate fires are notorious – they seem to occur every 10-20 years, causing major loss of life and widespread damage.  The lessons are learned for a while but unless the safety precautions are improved and then permanently monitored, and there is a change in culture that this is a continuous process that requires constant vigilance, not just putting in place a few improved measures at the time.  Big accidents include:

– Oppau, Germany, 1921 – 400 dead, 2000 injuries, 700 homes destroyed

– Texas City, USA, 1947 – 600 dead, 5000 injuries, 500 homes destroyed

– Toulouse, France, 2001 – 30 dead, 2000 injuries, 500 homes damaged

– West, Texas, 2013 – 14 dead, 200 injuries, 150 homes damaged

– Tianjin, China, 2015 – 163 dead, 798 injuries

“So despite lots of experience with these accidents, global learning is poor.  As well as putting much better safety mitigation measures in place and making company management embrace a top-down safety culture, communication between manufacturers and users of these and similar materials across the world is very poor – largely because embedding ensuring the users know about all the lessons from the past and bring in best practice is still not widespread practice.”


Trish Kerin, Director, IChemE Safety Centre, said:

“Tragically we have seen a massive explosion in Beirut, but even worse is that this is the latest in a long list of Ammonium Nitrate explosions that have occurred around the world.  We must do better to learn the lessons of the past, those lessons are written in blood.  This incident reminds us of the importance of process safety in our workplaces, including storage facilities.  We must implement and manage the controls to prevent and mitigate the consequences.”


Zsuzsanna Gyenes, Deputy to the Director IChemE Safety Centre, said:

“There have been several accidents and a few disasters in the ammonium nitrate fertiliser industry, and it is worthwhile to review these from time to time, beyond the regulation and practice changes which they triggered.  On 21 September in 1921, two consecutive explosions occurred in a silo in the BASF plant in Oppau, Germany, creating a 20m deep, 90x125m large crater.  The entire area was covered by dark green smoke and there were several additional fires and small explosions.  At the time of the event 4500 tonnes of ammonium sulphate nitrate compound fertiliser (ASN) were stored in the silo.  The explosion killed 507 people and injured 1917.

“Another tragic accident, involving two ships loaded with thousands of tonnes of ammonium nitrate and sulphur, occurred on 16 April in 1947, on the ship SS Grandcamp docked in Texas City, Texas, USA2. In that event, 500 people died and 3500 people were injured, which was 25% of Texas City’s population at the time.

“Exactly 80 years to the day after Oppau, a severe explosion occurred in a temporary storage for off-specification and downgraded ammonium nitrates at 10.17 a.m. on 21 September in 2001 at the AZF industrial site in Toulouse, France.  The detonation, felt several kilometres away, corresponded to a magnitude of 3.4 on the Richter scale.  A 7m deep crater (65x45m) was observed outside the plant and a large cloud of dust and red smoke drifted to the north-west.  The accident resulted in 30 fatalities, with up to 10,000 people injured and 14,000 people receiving therapy for acute posttraumatic stress.  The cost was estimated by insurers to be in the region of 1.5 billion Euro.

“More than 60 years after the Texas City disaster, a significant explosion of fertilisers shook the inhabitants of Texas again.  On the evening of 17 April 2013, a fire of undetermined origin broke out at the West Fertilizer Company in West, Texas, USA.  After their arrival, firefighters started to fight the fire when a detonation occurred.  Although the firefighters were aware of the hazard from the tanks of anhydrous ammonia, they were not informed of the explosion hazard from the 30 tonnes of fertiliser grade ammonium nitrate with a 34 percent total nitrogen content, which was stored in bulk granular form in a 7 m high bin inside the wooden warehouse.”


Ken Patterson, Editorial Panel member of the Institution of Chemical Engineer’s Loss Prevention Bulletin, said:

“Ammonium Nitrate is a hazardous chemical which has caused a string of accidents – indeed many of the world’s biggest industrial accidents.  For example, 300-400 tonnes of Ammonium Nitrate exploded in Toulouse on 21 September 2001 killing 29 people, including people off site.  Ammonium Nitrate was also the material which exploded in West Texas in 2013 when 15 people were killed and 160 injured.

“Ammonium Nitrate was the chemical involved in probably Europe’s worst industrial accident, the explosion at Oppau (Ludwigshaven) in Germany in 1921 when approximately 560 people were killed, when approximately 4,500 tonnes of ammonium nitrate exploded.

“Ammonium Nitrate is a chemical of such concern that it is specially mentioned in the EU’s Seveso Directive which regulates the storage and handling of all hazardous chemicals across the EU.

“The hazards of Ammonium Nitrate are extremely well known and the Health and Safety Executive had specific guidance on the storage and handling of Ammonium Nitrate in the 1980s.  It is always potentially unstable and becomes more unstable if its purity is compromised.

“Ammonium Nitrate requires a significant igniter.  The video evidence in Beirut showing the fire before the explosion, with fireworks apparently exploding all the time, would have provided an obvious source of ignition for the Ammonium Nitrate store.”


Dr David Slater, Honorary Professor, Cardiff University, said:

“Ammonium Nitrate is a common farm and garden fertiliser.

“As pure white crystals or prills (spheres) it is normally stable.

“If contaminated, usually with fuel oil, diesel etc. or degraded or with lots of impurities from manufacture, it is a highly dangerous solid explosive with TNT type effects.

“This means it detonates with a spherical supersonic blast wave.  These can have very high pressure differences across the shock front and its very sharp discontinuity in pressure is very damaging – called “brisance”.

“The observation of breaking of window glass at a 6-mile radius will allow a TNT equivalent estimate to be made of the size of the detonation (the first bang was an explosion but the second was a true detonation with the observed devastating effects).  A better estimate of the size will be available from a closer look at the damage patterns; but it looks initially that only a small fraction of the 2750 tons actually detonated – hundreds of tons of TNT equivalent, not thousands.

“The videos clearly show the blast wave and the characteristic brown red NO2 plume of smoke.

“Ammonium nitrate incidents are very common because most people think of it as harmless fertiliser.  It became the explosive of choice for many terrorist groups – easily obtained and utilised for nefarious purposes.

“The last major incident appears to have been in the Chinese port of Tianjin.

“It is dangerous because it is considered innocuous – not toxic etc.

“The oversight of the authorities was thus most likely due to ignorance rather than incompetence.

“It is an easy case to diagnose – obvious from the first videos before official confirmation.”


Mr Martin Goose, formerly HM Principal Specialist Inspector (Fire and Explosion) and formerly HM Principal Inspector of Explosives, of the Health and safety Executive (CV at, said:

What is ammonium nitrate?

“1. Used as a fertilizer.

“2. Used as an explosive when mixed with organic matter such as fuel oil to give ANFO (cheap explosive for quarrying etc. in dry conditions).  It can be used in more sophisticated explosives which overcome the fact that ammonium nitrate is water soluble.  They are called ‘slurry’ or ‘water gel’ explosives.

Is it explosive – why might this have happened?

“Wikipedia gives good background in the article on ‘Ammonium nitrate disaster’:

“Bagged ammonium nitrate can be kept clean.  Bulk ammonium nitrate just piled on a floor is more difficult to keep uncontaminated.  It is thought that molten ammonium nitrate puddles in a fire can be detonated should there be an impact from collapsing parts of a building structure even if there was no prior contamination of the ammonium nitrate.

Is there anything that you can tell from the footage of the explosion?

“It shows a very clear hemispherical shock wave propagating away from the explosion site.

Is there anything that you can tell from the extent of the damage and how away the blast was felt?

“Detailed examination of the type of damage and range at which it occurred can be used by experts to estimate the amount of explosive equivalent involved.  This can be greatly affected by atmospheric conditions at the time, particularly a temperature inversion, which can lead to damage at greater distances than would be expected normally and hence potentially overestimating the quantity of explosive involved.

Any other comments?

“Should refer to previous explosions of AN:

1. Oppau (

2. Toulouse (”


Dr Kate Norton-Hewins, Lecturer in the Cranfield Forensic Institute, Cranfield University, said:

“The open source video evidence posted on numerous social media sites supports the following:

“Shortly before 18:00hrs local a fire and series of small explosions in a dockside warehouse at 33.901353, 35.518835 which appear conducive with a fire amongst stored fireworks.

“A short while later a massive explosion, with large fireball and visible shockwave occurs, leading to extensive destruction and damage out to a significant distance.

“The large explosion is clearly a detonation rather than a deflagration (as in a fireworks explosion).  There is a clear shockwave travelling at high speed (likely <~2,000 ms-1) visible across the surface of the bay water and as a condensate cloud which abruptly appears radiating out from the epicentre and then vanishes.

“There were reports from Lebanese officials shortly after that claimed that a quantity of ammonium nitrate had exploded.  This was reportedly confiscated following the seizure of the MV Rhosus on 23 Sep 2013 when it was found to be carrying 2,750 tons of bulk ammonium nitrate.  The ammonium nitrate was discharged into dockside warehousing where it remained.

“There were reports on social media that officials stated that a fire had been started by welding work on the warehouse, which initiated the fireworks, which spread to the bulk ammonium nitrate.

“Ammonium nitrate (NH4NO3 ) is a white crystalline solid widely used in agriculture as a high-nitrogen fertiliser, and also as a component of mining, quarrying and construction explosives (where it is typically mixed with diesel oil to form ANFO (AN/Fuel Oil).  Ammonium nitrate is not normally acknowledged as a high explosive in its own right, being mixed with other components such as oils, aluminium powder etc. in its industrial explosive uses.  That said there have been many examples throughout modern history when bulk ammonium nitrate has, typically due to accidents/fires, exploded en-masse with significant disastrous aftermath.  These include:

“The Oppau Explosion (1921) 4,500 tonnes AN / AS

The Texas City ster (1947) 2,300 tons AN

The West, Texas, explosion (2013) 240 tons

The Port of Tianjin, China, explosion (2015) 800 tonnes AN / 500 tonnes potassium nitrate,

“A list of some ammonium nitrate ‘disasters’ can be found here:

“It is evident from the videos that the initial fire in the warehouse involved a quantity of fireworks, which typically explode and project burning material, spreading the fire.  The mass explosion was clearly a detonation, but the velocity of detonation appears to have been at the ‘lower end of the scale of velocities of detonation for high explosives’, probably in the region of 2,000 ms-1, which would be expected if a quantity of ammonium nitrate under-went deflagration-to-detonation transition (i.e. burnt to detonation).

“Ammonium nitrate has a TNT RE (relative effectiveness) factor of about 0.42, this equates 2,750 tons of AN to slightly more than 1 Kiloton of TNT.  The crater visible beside the remains of the dockside concrete grain silos the next morning is extremely large and, in my opinion (based on remote imagery only), is consistent with such a quantity of explosives having detonated.

“So, in summary: a large quantity of confiscated ammonium nitrate, stored unnecessarily, in a poor location, with poor safety procedures and mixed explosives storage, caught fire due to improperly controlled maintenance and burnt to detonation, leading to mass deaths and injuries.”


Mr Tony Ennis, Director of HAZTECH Consultants Ltd, said:

“Ammonium nitrate is a relatively safe material if stored correctly but can become dangerous and unstable if stored incorrectly.  It can detonate if exposed to heat and/or shock, particularly if in a confined space.  The risk increases if it is contaminated with e.g. fuel oil, alkalis or organic materials.

“It has an explosion efficiency of approximately 40% that of TNT i.e. 1 kg of ammonium nitrate will give an equivalent energy release to 0.4 kg of TNT.  Thus, 2,750 tonnes of ammonium nitrate would give an explosion equivalent to ~1,100 tonnes of TNT.

“This won’t be 100% efficient as an explosion but certainly equivalent to about 1,000 (a kilotonne) of TNT as a worst case.

“The presence of a large fire in the area could initiate an explosion, especially if the ammonium nitrate is contaminated or badly stored.  The white expanding cloud seen in the videos is the moisture in the air which condenses as the detonation shockwave moves through the air at the speed of sound.

“In the UK the storage of this material is covered under the Control of Major Accident Hazard Regulations (COMAH).  Guidance is available from the HSE in INDG30 ‘Storage & Handling of Ammonium Nitrate’.  The material should be in a well ventilated area and spaced out to prevent fire spread, HSE advice being not more than 300 tonnes per stack.  It should also be stored away from a list of other materials such as  flammable liquids, powdered metals, acids, chlorates, nitrates, zinc, copper and its salts, oils, grease, gas cylinders etc.”


Dr Rory Hadden, Rushbrook Senior Lecturer in Fire Investigation, University of Edinburgh, said:

What is ammonium nitrate?

“Ammonium nitrate is a commonly used chemical in fertilisers and also in explosives.  It is an oxidiser which means that it can enhance combustion reactions.  It does this by providing additional oxygen from the nitrate ion (which is a combination of nitrogen and oxygen).

Is it explosive – why might this have happened?

“Yes.  Ammonium nitrate will undergo an exothermic decomposition.  That means once it is heated the compound splits apart releasing energy.  This increases the temperature of the adjacent material which in turn increases the reaction rate.  A feedback loop is established and the rate of the reaction continues to increase.  Under some conditions this may result in an explosion (deflagration).  In this case it seems that a detonation occurred which is possible under the right conditions.  Although it is hard to ignite, ammonium nitrate can undergo a detonation if it is strongly heated in a confined space.  Contamination with impurities or other substances may promote these reactions.

Is there anything that you can tell from the footage of the explosion?

“Not really.  The shockwave is very visible indicating a detonation.

Is there anything that you can tell from the extent of the damage and how away the blast was felt?

“It is in general not really possible to do this unless you have good access to the debris and knowledge of the surroundings.

Any other comments?

“This is a very sad incident that highlights again the need for good practices in the production and storage of reactive materials.”


Prof Andrea Sella, Professor of Inorganic Chemistry, UCL, said:

“Ammonium nitrate is a major industrial chemical with two principal uses – as fertiliser and as an explosive.

“Poorly stored ammonium nitrate is notorious for explosions – for example in Oppau, Germany; in Galveston Bay, Texas; and more recently at West in Waco, Texas; and Tianjin in China.

“Explosions are typically detonations that cause huge damage due to the supersonic shockwave, which is clearly visible in the videos.

“Detonation of ammonium nitrate does not require additional fuel but is often set off by an initial fire which then causes the bulk material to blow.

“The orange plume above the explosion site is due to nitrogen dioxide, the toxic air pollution gas, and is a tell-tale sign of a nitrate-based explosion.

“This is a catastrophic regulatory failure because regulations on the storage of ammonium nitrate are typically very clear.

“The idea that such a quantity would have been left unattended for six years beggars belief and was an accident waiting to happen.”


Mr Trevor Lawrence, Senior Lecturer and expert in explosives and munitions at Cranfield Ordnance Test and Evaluation Centre (COTEC), Cranfield University, said:

What is ammonium nitrate?

“Ammonium nitrate is a substance used widely in fertilisers and also commonly as an oxidiser in home-made explosives.  Normally it needs the addition of a fuel to produce an explosive, but under some circumstances it can detonate.

Is it explosive – why might this have happened?

“Ammonium nitrate is hygroscopic and forms a hard crust when it absorbs water.  It degrades in storage with an exothermic reaction, so heat is produced.  If the ammonium nitrate ignites, and the hard crust confines it, then the burn wave can transition to a detonation by a process known as deflagration to detonation transition.

Is there anything that you can tell from the footage of the explosion?

“A burn transitioned to a large detonation.

Is there anything that you can tell from the extent of the damage and how away the blast was felt?

“Ammonium nitrate has a relatively low velocity of detonation therefore a long pressure pulse.  This causes a ‘lift and heave’ effect, which added to the structural damage.”


Prof Clifford Jones, Visiting Professor in Chemical Engineering, University of Chester, said:

“Ammonium nitrate is a high exposive, meaning that propagation of combustion is supersonic.  This contrasts with, for example, a petrol bomb, where propagation is subsonic.  That is because the oxygen required for ammonium nitrate to explode is supplied not from the atmosphere but from within the ammonium nitrate structure itself, and that is referred to by experts as ‘intra-molecular oxygen’.  A consequence of the rapid propagation is the high overpressure, the factor in the deaths and injuries.

“There have been many cases of ammonium nitrate explosions.  One of the best known was in Texas City in 1947, when there were > 580 deaths.  A much more recent one was at Waco Texas in 2013, when there were 15 deaths and 160 injuries.”



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