Compressed Gases

Question 1

What are the states of matter

Answer 1

Matter exists in three physical states at normal temperature and pressure. They are:
Solid
Liquid
Gas

Question 2

Define a solid physical state

Answer 2

A solid object can be though of as one that tries to keep a definite shape and a definite bulk, or volume. In brief it has a fixed volume and shape.

Question 3

Define a liquid physical state

Answer 3

A liquid has a definite volume, it is almost impossible to pack it into any smaller space. A liquid will take on the shape of the container into which it is poured. In brief it has a fixed volume and variable shape.

Question 4

Define a gas physical state

Answer 4

A gas has neither a definite shape nor a definite volume. It expands to fill any container completely, regardless of the size or shape of the container. In brief it has no fixed volume and variable shape.

Question 5

Define changes in states of matter

Answer 5

At certain pressures and temperatures all matter will change its state. Liquefying (melting) and vaporisation describes the changes from a solid to a liquid to a gas. Condensing and freezing describe the changes from a gas to a liquid to a solid.

Question 6

What two terms are important when understanding how gases behave

Answer 6

Vapour density

Explosive limits of gases

Question 7

Describe vapour density

Answer 7

Vapour density is the ratio of the density of a gas or vapour compared with the density of air.
Air is assigned a vapour density of 1.
Therefore if the vapour density of a gas or vapour is less than 1, the gas is less dense, or lighter than air and will rise.
On the other hand if the vapour density is greater than 1, the gas is more dense or heavier than air and it will fall.

Question 8

Ways gases can be stored in cylinders

Answer 8

Compressed gases
Liquefied gases
Cryogenic gases

Question 9

Common gas cylinder labels

Answer 9

Poison gas.
Poisonous and flammable - two diamonds on label.
Oxidising agent.
Non flammable.
Flammable.

Question 10

Process of clamping off ruptured gas lines

Answer 10

SOG #12
Appliance pump engaged, with crew member standing by with charged line.
Full level D, with BA donned.
Adequate hearing protection fitted.
Correct gas clamp selected.
Correct tools selected for digging around impacted area.
Clamp supply side for service pipeline.
Clamp both sides for main distribution as they’re generally ring mains.

Question 11

How to deal with fire exposed acetylene cylinder

Answer 11

Acetylene is extremely dangerous with a flammable range of 2.5% to 80%.
Therefore and exclusion zone of 200m should be set up.
Cylinder should be cooled with water for 1hr and checked for temperature drop. Continue cooling if no change.

Question 12

What is BLEVE

Answer 12

Boiling liquid expanding vapour explosion.
When a cylinder is involved in a fire the contents expand so much the cylinder can no longer contain the pressure and ruptures due to structural fatigue caused by intense heat. This rupture releases large amounts of liquid gas that simultaneously expands into a huge vapour cloud and burns as a fireball.

Question 13

How can BLEVE be anticipated

Answer 13

Flame impingement.
Discolouration of the gas cylinder.
Distortion of the gas cylinder.
Activation f the relief valve (apart from normal rises in the ambient temperature level).
Relief valve sound becoming increasingly louder i.e. higher pitched.