Petrochemical or gas fuelled fires lead to extreme temperature transients within minutes of a fire commencing. These extremes can exert enormous thermal forces on steel and concrete clad elements. In the latter it can lead to severe spalling with subsequent exposure of the steel reinforcement bars. Such rapid rise and intense fires at a processing facility can create the potential for highly destructive conflagrations.
The Esso Longford gas explosion of September 25, 1998 was one of Australia’s most catastrophic industrial accidents which occurred at the Esso natural gas plant in the state of Victoria. The explosion killed two workers and left a further eight injured. The fire at the plant lasted for two days and the state of Victoria was left without its primary gas supplier. The state gas supply was shut down and gas supply did not resume till 20 days later. The gas supply shortage devastated Victoria's economy with losses estimated at around A$1.3 billion over that period.
Such accidents bespeak the need to properly assess and evaluate the risks involved, and to have in place fire and blast protection measures that can contain these types of fire incidents, effectively and expeditiously. Whilst design, location, spacing between plant equipment, and spill containment are fundamental ways of mitigating fire damage, other protective measures are required -, Active and Passive. Active systems rely on the use of monitoring equipment, hose reels, pumping and piping equipment to deliver the water and/or chemicals necessary to combat the fire. Passive fire protective systems are specially engineered to SHIELD essential structures, plant equipment and services from fires, and to significantly enhance their capacity to maintain structural stability and integrity throughout the fire event. HYDROCARBON FIREPROOFING achieves HYDROCARBON FIREPROTECTION by means of hydraulically setting materials applied to the perimeter of structural steel members and vessels in variable thicknesses to the desired period of fire protection (up to 4 hours).
Jet fires are defined as a leak from a pressurized vessel, such as an LPG tank, or between pipe flanges which ignites and forms a burning jet which impinges on other equipment causing severe damage. For LPG, the jet length is estimated to be about 150 times the jet orifice diameter; meaning that a jet from a 50 mm hole could produce a burning jet about 10 m long!
So far the standards chosen by LAF to cover rapid rise or hydrocarbon fires have been ASTM E1529, UL 1709, RWS, RABT and HCmod. Jet Fire test exposes the test specimen in front of a shallow chamber, to a jet flow emanating from a nozzle with high erosive forces. The sonic velocity gas jet reaches velocities of 100 ms-1 and reduces to 60ms-1 at the back of the chamber. The average heat flux is 240kWm-2 and the maximum heat flux 300 kWm-2. The test arrangement is intended to apply a heat loading equal to a 3 kgs-1 natural gas (60bar, 20 mm nozzle orifice) jet fire released 9 m from a target. The Flame temperatures will be dependent primarily on the fundamental combustion properties of the fuel and may not increase significantly with increasing gas flow rate.
LAF will cover Jet Fire scenarios through testing to ISO22899-1(2007), Test Procedures for Jet Fires, and be carried out under the supervision of an “approving authority” such as DNV or Lloyds etc.