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1、Acetylene Cylinders Scope today Cylinders in fires Acetylene a special problem Why is UK different? What can be done about it? Research Cylinders in Fires All gas cylinders may explode in fires Increasing gas pressure overcomes reducing steel cylinder shell strength at 300oC Cooling restores shell s
2、trength and reduces gas pressure But Acetylene might re-heat Acetylene is fuel gas of choice Flame temperature of 3150oC and lighter than air Carbon-Carbon triple bond reactive, not unstable 3 x Acetylene reactions of interest in fire Decomposition not spontaneous!- needs 350oC C2H2 + HEAT 2C + H2 +
3、 more HEAT Severe shock to a HOT cylinder? Acetylene (C2H2) Acetylene Cylinders Porous monolithic mass Acetylene dissolved in a solvent small cells act as flame arrestor Designed to stop decomposition Steel heat treated Low fill pressure But mass is a heat insulator Acetylene cylinders have a hard l
4、ife! the myth of cold impact effect Acetylene cylinder testing Drop test Elevated temperature test Backfire test Impact resistance test 90g Plastic explosive charge Impact stability of Acetylene cylinders Impact resistance test Test protocol requires cylinder to dent by 25% of its diameter. Example
5、shown about 50% Porous mass not damaged No damage other than dent itself No cracks No sharp-edged deformations No indication of decomposition Cold Shock Gas expert opinion For F+RS, Police and Highways Agency “Mechanical shock alone to a cold Acetylene cylinder, which remains intact and has not been
6、 exposed to fire, cannot initiate decomposition.” Acetylene vs Propane Propane Acetylene Cylinder content (Typical) 47Kg 8Kg Gas density 1.55 0.9 Flame temp with O2 2500 3200 Flammability limits in air 2.2 - 9.5% 2.5 - 81% Max fill pressure (Bar) 10 18 Cylinder burst pressure (Bar) 67 105 Relative B
7、TU yield 1 4 Cu Metres Oxygen needed 4 1 Special risk BLEVE Decomposition Cutting? Yes Yes Brazing? Yes Yes Welding No Yes UK protocol for DA in Fires is different! Since 2003/2004 Initial 200m hazard zone whilst facts established Zone reduction based on dynamic risk assessment 24 hour precautionary
8、 cooling Acetylene cylinder may not be moved or vented BUT often 200m EXCLUSION zone held for 24hours causes massive disruption! Why the UK protocol became so? Death of John Wixey 1987 HSL Experiments in 1994 Fire Service training content Myth and folklore! The London improvement In 6 years 04 to 09
9、 London had:- 543 Cylinder incidents 102 incidents really involved Acetylene after all 4 DA cylinders exploded ALL IN FIRE, NOT AFTER. NO cylinder re-heated after 1 hour cooling 437 wet tests passed on 140 cylinders all found at ambient temperature! From August 07 to Oct 09:- London F+RS reduced inc
10、ident frequency from 14 to 25 days and average disruption time from 19 to 2.67 hours! Problem solved! why not elsewhere? BAM Research German Federal Institute of Materials Science World renowned acetylene experts Independent contract research commissioned by BCGA, HSE, DfT, TfL What cooling period i
11、s required for an Acetylene cylinder to be sure any decomposition is over and cannot re-start? Screening: Acetylene only Explosive decomposition occurs at about 350 C ruining the pressure transducer Conditions as before, but start pressure 10 bar Research What conclusions to date? Model works and ca
12、n be interrogated Mass type makes no difference No decomposition until 350c Polymerization occurs 300c but is pressure reducing We assume DA cylinders which explode in fire do so because of decomposition? More likely simple over pressure research Phase III work Full scale cylinder tests (at Horstwalde!) Summary Acetylene cylinders present a special hazard UK procedures have been over-cautious Good research progressing on heat transfer Cold impact case proven Acetylene is needed and is safe if stored, transported and used correctly
