Accidental Ammonium Nitrate Explosions

Paul Somerville and Ryan Crompton, Risk Frontiers

Insurers are gearing up for what is likely to be one of the most expensive insured cargo and port infrastructure losses ever from the Beirut explosion, on a scale at least as large as the one resulting from the explosions at the Chinese port of Tianjin in 2015 (800 tonnes, 173 deaths). It is expected that Lebanon’s second port of Tripoli, believed to be operating at just 40% capacity on account of COVID-19, will become the country’s main gateway for both emergency supplies and normal trading.

The accidental ammonium nitrate explosion in Beirut serves as a reminder of how frequent and deadly these events are. A timeline and description of events since 2000 is shown in Figure 1. The Wyandra, Northern Territory event of 2014 is shown in Figure 1 and is one of three Australian events, described later, that appear in the Han (2016) catalogue.

Timeline of accidental ammonium nitrate explosions.
Figure 1. Timeline of the largest accidental ammonium nitrate explosions in the world since 2000.  Source: VisualCapitalist.

We analysed Han’s (2016) catalogue which lists 79 events since 1896, 42 of which occurred in the United States, to assess their frequency of occurrence. Since 1900, they have occurred at a uniform rate of about 0.75 per year, with an increase to about 1 per year since 2000. To the extent that Han’s list is incomplete, these rates are underestimated. Han (2016) notes that the ammonium nitrate that exploded in the 1947 Texas City (Galveston) event was coated with wax to prevent caking.  Practices introduced in the 1950s eliminating the use of wax coatings yield ammonium nitrate, used in fertilisers, that contain less than 0.2 percent combustible material. This practice does not appear to have impacted the frequency of events.

We also analysed the Wikipedia catalogue of 36 events, which lists both size (tonnes) and deaths, to assess the relation between size (tonnes) and number of deaths, shown in Figure 2. To first order, Log10 Deaths = 0.85 log10 Tonnes. Four notable events on the left panel of Figure 2, clockwise from top left, and labelled by numbers of deaths, are the 1921 Oppau, Germany event (450 tonnes, 561 deaths), the 1947 Texas City (Galveston, U.S.) event (2906 tonnes, 581 deaths),  the 2020 Beirut event (2750 tonnes, 220 deaths), and the 1947 Brest, France event (3000 tonnes, 29 deaths).

The relationship between size and deaths from ammonium nitrate explosions.
Figure 2. Relation between size (tonnes) and deaths from accidental ammonium nitrate explosions on linear (left) and log (right) scales. Several zero values on the axes of the log plot actually represent zero values: the 2004 North Korean event of 162 tonnes had no reported deaths.

Australian-based company, Orica, the world’s largest provider of commercial explosives and blasting systems to the mining, quarrying, oil and gas and construction markets, has a stockpile of ammonium nitrate up to four times the size of the one in Beirut. There are many stockpiles in Australia but Orica’s Kooragang Island plant has received a lot of media attention.

Between 6,000 to 12,000 tonnes are currently stored at Orica’s Kooragang Island plant in the Port of Newcastle, which produces approximately 400,000 tonnes each year. This plant is located 3 km from Newcastle’s CBD and 800 m from residents in Stockton. Up to 40,000 people live in what would be the ‘blast zone’ if there were to be an explosion. Orica state that they follow strict safety protocols and ensure that the ammonium nitrate storage areas are fire resistant and built exclusively from non-flammable materials, with no flammable sources within designated exclusion zones. The operations on the Kooragang Island site, which has been in operation for 51 years, are highly regulated to state and federal standards. The site’s safety management systems, security arrangements, and emergency response procedures undergo a strict auditing and verification process by SafeWork NSW. The Kooragang Precinct Emergency Sub Plan can be found here.

The safety of ammonium nitrate was previously highlighted in South Australia in 2013, when concerns were raised about the location of the Incitec Pivot fertiliser plant at Port Adelaide following the West, Texas, explosion of 2013 involving 240 tonnes of chemical that killed 15 people in a 50 unit apartment block. In 2013, the South Australian Government made an agreement with Incitec Pivot to move its plant away from the heart of Port Adelaide, because it posed an unacceptable risk to residents of a proposed major development there. The company moved its operations to a location further from the centre of Port Adelaide to Gillman in 2018. According to SafeWork SA, all 170 of the ammonium nitrate storages in the state are heavily regulated, heavily controlled and monitored.

Figure 3. Left: Incitec Pivot plant, Port of Adelaide; Right: Orica Kooragang Island plant.

In the remainder of this briefing we describe three Australian accidental explosions, all involving trucks.

Taroom, Queensland, 30 August 1972

A truck explosion occurred near Stonecroft Station on Fitzroy Development Road in August 1972. The truck and trailer were carrying 12 tonnes of ammonium nitrate. The truck experienced an electrical fault and caught fire north of Taroom. After the driver stopped and parked the burning truck, two brothers from a nearby cattle property who saw the fire rode up on motorbikes to assist. The three men were killed when the truck exploded at around 18:15. The explosion destroyed the prime mover and trailer, leaving a crater in the road 2 m deep, 5 m wide, 20 m long. Parts of the truck and trailer were scattered up to 2 km away. The explosion burnt out more than 800 hectares (2,000 acres) of surrounding bushland. The explosion was heard and shook houses 88 km away in Moura and 55 km away in Theodore.

Wyandra, Queensland, 5 September 2014

On September 5, 2014, an ammonium nitrate truck explosion (Figure 4) occurred near Wyandra, about 75 km south of Charleville in south-west Queensland, Australia. The truck carrying 56 tonnes of ammonium nitrate for making explosives rolled over a bridge and exploded, injuring eight persons including the driver, a police officer, and six firefighters. Rescue crews were trying to extract the driver from the truck when they found out there was ammonium nitrate inside. They were making a mad dash from the truck when it exploded.

The prime mover caught fire about 9.50pm and the driver steered off the highway, causing it to hit a guard rail near the Angellala Creek Bridge and roll onto its side in the dry creek bed. The crash led to two explosions occurring at 10.11pm and 10.12pm. The blast was so powerful that the truck disintegrated, destroying two firefighting vehicles along with it and causing catastrophic damage to the Mitchell Highway. Two road bridges were destroyed (Figure 5), one of the railway bridge spans was thrown 20 m through the air, and a major section of the highway was missing. Geoscience Australia recorded the explosion as a magnitude 2.0 event, and coincidentally, 20 minutes after the explosion, a magnitude 2 earthquake was recorded 55 km south of Charleville.

Emergency vehicles damaged by the Wyandra truck explosion. Queensland Police Service
Figure 4. Emergency vehicles damaged by the Wyandra truck explosion. Queensland Police Service.

The dangers posed by the remaining ammonium nitrate led to a 2km exclusion zone around the site for a number of days. The large crater formed by the blast closed the highway necessitating detours of up to 600 km, including a 100 km detour to Cunnamulla along the Charleville-Bollon Road. In April 2015, the $10 million tender to reconstruct the highway and bridges were awarded and the construction work took place between June and November 2015.

Damage to bridges caused by the Wyandra explosion.
Figure 5. Damage to bridges caused by the Wyandra explosion. Queensland Police Service

Queensland Transport Minister Scott Emerson noted that there are rules in place relating to signage and the particular routes that are allowed to carry dangerous goods and that he would be talking to police about whether anything was done wrongly. However, Assistant Fire Commissioner Dawson dismissed concerns that such a volatile material was being carried in trucks. “Not so much a worry; this product – and trucks like this very same truck – travel these roads every day,” he said. “Every day they’re out there and they don’t go bang. Something’s happened to bring this truck in a situation, which has possibly mixed the product on the back of the truck – maybe with the diesel fuel, the impact of the initial [crash] when it goes off the road – so those circumstances have had more of a connection to the end result. You’d be surprised – there’s a lot of these trucks – they do it very safely and very effectively.

On January 10, 2019, the Queensland State Government launched a lawsuit in the Brisbane Supreme Court claiming more than $7.8 million in damages, the estimated cost of building a temporary detour, and inspected the area to ensure it was safe as well as replacing the road and railway bridge. It was holding the trucking company, Kalari Proprietary Limited, road train driver Anthony David Eden and insurer Dornoch Limited responsible for the repair bill.

Ti Tree, Northern Territory, 18 November 2014

A road train consisting of three flat-bed trailers carrying ammonium nitrate fertiliser exploded in Ti Tree, NT on November 19, 2014 (Figure 6). Witnesses at the Ti Tree roadhouse, 200 km north of Alice Springs, saw a fire igniting on the left-hand side of the rear axle of the rear trailer. The road train driver inhaled fumes as he desperately unhooked the burning trailer of explosive ammonium nitrate from his truck on the Stuart Highway at Ti Tree. Moments later the trailer exploded with a loud bang, startling residents more than several hundred metres. The driver had towed away the two other trailers of ammonium nitrate. No-one was injured.

Police went door-to-door to evacuate residents to the school and establish a 1 km exclusion zone. Sixty to eighty people were evacuated to the school at the northern end of town at 10:30 pm, and were allowed to go home at 1:30 am but there was still a 300 m exclusion zone. At 2:00 am the fire crew declared the fire ‘safe’ and Stuart Highway was reopened.

Figure 6. Ti Tree explosion (left, Nicolai Bangsagaard) near the Ti Tree Roadhouse (right, Olivia Ryder).