AS/NZS5601.2.2022 Clause 3.1.8
AS/NZS5601.2.2022 Clause 3.1.8 allows the use of a “vapour barrier” as an acceptable technical option to achieve separation clearance requirements within the controlled area.
Vapour barriers can be used to shield vulnerable areas from exposure to leaking gas, acting to separate gas concentrations from possible ignition sources.
This is a recommended solution for current model vehicles with openable compartments in close proximity to gas cylinders.
In recognition that openable compartments typically in use in current industry products are likely to be significantly affected by the new controlled area application, Caravan Industry Association of Australia in collaboration with its member State Associations commissioned a gas flow modelling project to identify vapour barriers that could be used to shield openable compartments that would otherwise sit within the controlled area.
The basic concept of the vapour barriers is shown in the diagrams below.
The Vapour Barriers design requirements are laid out in AS/NZS1596.
The way it works is as follows. LPG is heavier than air and does not dissipate. In the interest of safety we need to prevent the vapour from resting in the percentage range between the lower explosive limit (LEL) and the upper explosive limit (UEL) gas to oxygen ratio. In the event of a leak the vapour will hit the vapour barrier and fall (being heavier than air) air movement will disperse the vapour.
In calculating the correct distance from an ignition source we use straight lines!
For example: If the distance from gas valve to the vapour barrier edge is 600mm and the barrier edge to locker opening is 600mm – Each straight line measure is 600mm.
We add the 600 + 600 so, distance from gas valve to opening equals 1200mm