Lecture 9 Flashcards
What were early examples of explosive accidents related to?
- ## A lot of accidents involved the confinement / storage of propellant
Delft Thunderclap in 1654 in the Netherlands
- Over 100 people died including painter Carel Fabritius and nearly all his work
- Approximately 30 tonnes of black powder stored in barrels in a cellar
- Thought to be ignited by a lamp during a watchman’s inspection
- The lamp had an open flame which ignited a small amount of gunpowder
6/12/1917 Halifax
- In Canada the SS-Mont-Blanc collided with the SS Imo at ~1 mph.
- It was carrying picric acid, TNT, guncotton and benzene
- The collision ignited the benzene and 20 mins later it exploded.
- Detonation was equivalent to around 3 kT of TNT
- The force of the collision accidentally ignited some of the benzene which just burns and they couldn’t stop it burn.
- The heat generated from the fire possibly caused the detonation of the explosive
- TNT is not a sensitive secondary explosive but the presence of guncotton (primary explosive) explains how the TNT could have detonated.
S5 Richard Montgomery
- Ran aground off the Kent Coast in 1944
- Still loaded with equivalent to 1.4 kT of TNT
- They didn’t want to tamper with explosives so they left them.
As TNT is a secondary explosive, they thought it wasn’t a big deal. - However, there is concern about redox reaction occurring with copper to form copper azide which is much more sensitive.
Example of a tertiary explosive involved in an explosive accident.
- In 1921 a plant in Oppau, Germany was producing a mixture of ammonium sulfate ((NH4)2SO4) and ammonium nitrate (NH4NO3)
- To break up and remove the hygroscopic plaster-like substance pickaxes and dynamite were used!
- This was considered ‘safe’ as the mixture was only expected to explode at >2:1 NH4NO3:(NH4)2SO4 and the mixture was wet.
- Researchers were working on drying the mixture so it became more sensitive and was detonated
What type of explosive is ammonium nitrate?
It is a tertiary explosive except when it’s in the presence of fuel
What does hygroscopic mean?
This is when a material absorbs water very readily from surroundings which is really hard and difficult to mine
Beirut Explosion August 2020
- Initial reports were of a huge explosion from the port area (17:55)
- Initial fire in a warehouse 🡪 firefighters reported “something wrong” and a “crazy sound”
- The first explosion was relatively small and occurred at 18:07 equivalent to around 2 tons of TNT
- Second explosion 30 seconds later was huge and equivalent to 0.5-1 kT of TNT
What caused the Beirut explosions?
- The first fire was likely ignited by a welding door in the warehouse.
- This ignited some of the stored fireworks containing black powder or flash powder.
- The fireworks were contained in a small area so it is theorised this is why they detonated rather than deflagrated.
- The main detonation consisted of 2.7 kilotons of ANFO
What is fuel oil?
- Fuel oil is a diverse mixture of different hydrocarbons so it is difficult to calculate ANFO oxygen balance
- It mostly consists of CH2 units
Give the equation for a theoretical fuel of any C length using ANFO
- 3NH4NO3 + “CH2” → 7H2O + CO2 + 3N2
- This gives an oxygen balance of 0
Assuming that we’re fully oxidising, what would be the ideal mass of ANFO to form CO2?
- Determine the balanced equation
- Calculate the total idealised MW of the reactants (Don’t worry about the fuel oil C chain length, only account for 1 but account for all ANFO)
- Calculate the % weight of ANFO (MW of ANFO / MW of total idealised)
- Calculate % weight of fuel oil (MW of fuel oil / idealised MW)
- This provides an approximate ideal composition by mass for ANFO
What is the true oxygen balance of ANFO?
- The true oxygen balance of ANFO is slightly negative as fuel oil is really a mixture composed primarily of CnH2n+2
What does a red-coloured plume indicate?
- the formation of NO2 gases
How was the blast wave speed estimated in the Beirut explosion?
Audio and video data collected from social media coverage
Origins of the cargo in the Beirut explosion?
- The MV Rhosus attempted to carry more ANFO but got damaged by the weight and stuck
- It was stored in a warehouse where the explosion occurred
- The documentation regarding the contraband wasn’t done correctly
- Several warning letters were set to authorities but ignored
What caused the explosion in the Buncefield explosion?
- On 11th December 2005 a fire in a Hertfordshire oil storage terminal led to an explosion
- A fuel-air explosion occurred
- Oxygen was used from the air to detonate the explosion which meant the K-W don’t apply
- The fuel was petrol (C4C12)
What is a fuel-air explosion?
- When oxygen from the air is used to cause an explosion (the oxidizer)
- This can cause aerosolised fuel can explode
- KW rules don’t apply
When are fuel-air explosions used?
They are largely used in the military as large thermobaric weapons
Thermobaric weapons
- The fuel is ethylene oxide or propylene oxide
- The reaction happens very quickly
- A spark initiates the explosion
- The detonation point doesn’t have to be accurate as it consumes oxygen from the air around it so the reaction will propagate across
Combustion of propylene oxide
C3H6O + 4O2 → 3CO2 + 3H2O
How did the Buncefield explosion start?
- A level controller on an oil tank failed overnight meaning fuel filled until it overflowed
- The vapour cloud enveloped the whole site very quickly
- ## Unknown ignition source as nobody was on site when the explosion happened
What was learned from the Buncefield explosion?
- ‘High integrity’ containment for fuels are required
- Incorporate a secondary containment system (another layer around storage tanks)
- Better detection systems/alarms for flammable gases now used
- Investigate possible ignition sources further from containment site
