Service Delivery 4

Compressed Gases

Aim

To familiarise students with the procedures for dealing with compressed gases.

Learning Outcomes

• State the properties of compressed gases

• List the hazards and appropriate operational procedures for incidents involving compressed gases.

At the end of the session students will be able to:

Introduction• Compressed gases are stored, transported and

used in a variety of ways

• A particular gas may be flammable, explosive, toxic or possess a combination of these features

• Operations at incidents involving compressed gases will vary according to volume, method of containment, specific properties of gas involved and nature of surrounding exposures.

Storage

Extent of threat depends on;

• Nature of the gas

• Quantity of the gas

• Nature of premises concerned and surrounding exposures.

Storage

Cylinders

Industrial gases colour code BS 349

Medical gases colour code BS1319

Threat from fire

Flying fragments up to 100 metres

Rapid spread of fire between adjacent cylinders.

Safety devices

Bulk;

Pressure relief valve

Emergency control valve.

Safety devicesCylinders;

• Pressure relief valve

• Bursting discs

• Fusible plugs.

Storage.Bulk storage; • Spheres

Storage.Bulk storage; • Tanks

B.L.E.V.E. Boiling Liquid Expanding Vapour Explosion

• Hydrocarbon flame burns up to 2,000 °C

• Steel weakens as temperatures exceed 350/400 °C

• Dry wall attains temperature of 300+ °C

• Severe hazard unless massive cooling.

B.L.E.V.E. Firefighting procedures

• If no risk to life or property, give serious consideration to a “non-attack” strategy

• Where only property is at risk, it may still be necessary to consider a “non-attack” strategy.

B.L.E.V.E. Firefighting procedures

• If attacking the fire, immediate cooling must be undertaken, concentrating on the exposed vapour space

• Personnel should be fully briefed and made aware of the hazards.

LPG Liquified petroleum gas

• Colourless• Liquid (under pressure or low temperature)• Flammable• Explosive• Odourless (has stenching agent added)• Heavier than air• High co-efficient of expansion.

LPG

Butane Propane

• Flash point -60 °C

• Boiling point -6 °C

• Explosive limits 1.5% - 9.0%

• Flash point -104 °C

• Boiling point -42 °C

• Explosive limits 2.4% - 9.5%.

Gas release

An unignited gas release can present a number of problems;

• Large gas cloud

• Possible ignition sources

• Environmental hazards.

Leakage of LPG without ignition

Shut off leak at source

Prevent ignition

Safe dispersal of gas/vapour cloud.

Dealing with vapour clouds

• Use of fog branches / monitors

• Ground sprays projecting a flat fan spray

• Ground monitors set at 45 degrees spray pointing straight up

• Gas detectors to monitor effectiveness.

Gas dispersal

• Using hand held branches, under sufficient pressure, flames and/or gas may be channeled away

• Using portable monitors small leaks may be entrained into a low pressure area in the centre of the spray and directed to a safe area.

Gas dispersal

• Several monitors can be positioned around a leak forcing gas upwards

• Water curtain spray branches can be used to protect areas from gas and perhaps provide a safe escape.

Access and location

Isolation is the most effect method of eliminating any danger from an uncontrolled gas release.

Access and location

• Evacuate the area

• Eliminate any ignition sources

• Attempt a controlled isolation

• Render the area safe.

If unignited;

Access and location

• Evacuate the area

• Provide personal and structural protection

• Controlled isolation.

If ignited;

Leakage with ignition

Do not extinguish flames until outflow has been stopped

Reduce areas of burning liquid by applying foam blanket

Secure additional cooling

Cool supporting structure

Keep cooling water away from valves to prevent freezing

Monitor pressure relief valves.

Acetylene

• Colourless

• Non-toxic

• Highly flammable

• Ethereal (anaesthetic ) odour

• Industrial - garlic smell / lighter than air

• Decomposes in absence of oxygen or air

• Ignited from static charge.

Acetylene

• Spontaneous ignition temp 335° C

• Critical temperature 35.2° C

• Flammability limits 2.5% - 80%

• Flame temperature 2325° C.

Acetylene cylinders

• Seamless steel cylinders

• Welded steel cylinders

• Colour coding

• Storage (porous mass, acetone )

• General.

Acetylene cylinder incidents

• Leaks from the cylinder safety device (if fitted ) or valve associated equipment, whether the gas has been ignited or not

• Flashback from a torch into cylinder

• Cylinders in vicinity of fire and subjected to heat

• Shock.

Unignited leaks

Urgent assessment of volume released - Time and rate of discharge in relation to capacity of cylinder

Prevailing winds

Total areas involved

Ignition hazards

Attempts to close leak without igniting gas

Ventilate building

150 metre ‘hazard zone.’

Summary of LPG

• Full firefighting kit to be worn

• Be aware of and use other P.P.E

• Liquefiable gas

• Very low flash point

• Heavier than air

• Stored under pressure.

Summary of LPG

• Flame impingement

• Container over-heating

• B.L.E.V.E.

Also be aware of explosion risk due to;

Summary of LPG

• Sources of ignition

• Wind direction

• Vapour collecting (low points)

• Vapour dispersal.

Consider;

Summary of acetylene

• Full firefighting kit to be worn

• Be aware of and use other P.P.E

• Minimum number of personnel inside the 150 metre hazard zone

• Do not lift any cylinders where decomposition is suspected

• Do not drop cylinders.

ConfirmationAssessments will be based on this lesson and the corresponding study note

Learning Outcomes

• State the properties of compressed gases

• List the hazards and appropriate operational procedures for incidents involving compressed gases.

THE END