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 strength 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 > 350oCC2H2 + HEAT → 2C + H2 + 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 life! – 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 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 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 BTU 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 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 1987HSL Experiments in 1994Fire Service training

contentMyth and folklore!

The ‘London improvement’

In 6 years ‘04 to ‘09 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 incident 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 is 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 can 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

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