Explosions 9 Flashcards
Why is it difficult to calculate the ANFO oxygen balance?
because fuel oil is a mixture of hydrocarbons
What are the detonation products of ANFO?
NH4NO3 + CH2 –> H2O + CO2 + N2
What is ideal and true oxygen balance for ANFO?
Why is the detonation process of ANFO difficult and what indicates this?
idealised oxygen balance of 0 (fully oxidised) gives approximate ideal composition by mass for ANFO is 94% NH4NO3 and 6% fuel oil (might want to sacrifice some ammonium nitrate to introduce more fuel so it is made more sensitive)
true oxygen balance is slightly negative as fuel oil is a mixture
explosion smoke plume is red which is likely caused by NO2 gas - shows more complicated than just producing H2O, CO2 and N2
How are blast waves estimated?
blast wave speed estimated using social media coverage (audio and video data collected and the timings examined in combination with known locations)
approximate TNT equivalent mass (W):
log(ta/W(1/3)) = 0.07log(Z)5 – 0.057log(Z)4
where:
ta = time of arrival
Z = R/W(1/3)
R = radius from source
What happened in 2013 in Beirut port?
in September 2013, MV Rhosus was carrying ANFO from Georgia to Mozambique and took on more cargo in Beirut
More cargo = damaged beyond repair = ship owner bankrupt = Beirut port authority seized ship = stored in port warehouse = 6 warning letters sent warning about explosives = they exploded
take home message - avoid miscellaneous contraband storage in ports
What happened in Buncefield Explosion?
What four lessons were learnt?
December 20015 a fire in Hertfordshire oil storage terminal led to explosion
Shockwaves felt as far as Surrey
Flames seen in Lincolnshire
A level controller on an oil tank filled overnight meaning fuel filled until it overflowed through vents at top - liquid petrol didn’t go far but vapour cloud enveloped whole site and unknown ignition source.
Explosion caused by fuel-air explosion - fuel was petrol (C4 - C12 hydrocarbons roughly normally distributed so peaks at octane (8))
1 - high integrity containment for fuels are required
2 - incorporate a secondary containment system (another layer around storage tanks)
3 - better detection systems/alarms for flammable gases now used
4 - investigate any possible ignition sources further from containment site
Define a fuel-air explosion
a finely divided (aerosolised) fuel can explode very rapidly with some initiation.
oxidiser is O2 from air
K-W rules do not apply
What are fuel-air explosives used in military as?
How does this work?
thermobaric weapons
fuel (ethylene oxide or propylene oxide) as a fine spray that is initiated by oxygen from air:
C3H6O + 4O2 –> 3CO2 + 3H2O
Don’t have to be super accurate with point of detonation as long as it is close - a shockwave is generated that is sent out that can cause damage
