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Gas information sheet 47: Vent terminal exclusion zone for ignition sources

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This information sheet has been prepared to reduce confusion in the determination of the size of the vent terminal exclusion zone for ignition sources.

A typographical error, in the Australian and New Zealand Standard AS/NZS 5601.1:2013, clause 5.11.5.9 Vent terminal location, Figure 5.3, has caused this confusion.

Current description

AS/NZS 5601.1:2013 clause 5.11.5.9 Vent terminal location states the following:

A vent terminal shall be located where gas discharge will dissipate without entering buildings or creating any hazard. The point of discharge shall-

(c) in cases where there is any object (e.g., wall, ground, etc.) in the direction of discharge and within the exclusion zone of Figure 5.3, be located so there is no ignition source or opening into a building within a sphere of radius r (of Figure 5.3) centred on the vent terminal discharge point.

 

Figure 5.3

Figure 5.3

 

Notes:

  1. T= [Vent terminal diameter (mm)] / 50
  2. The exclusion zone shown above depicts a space consisting of a cylinder in the discharge direction and a hemisphere in the opposite direction of discharge from the vent terminal discharge point.
  3. The exclusion zone only applies up to 200 kPa. For pressures exceeding 200 kPa, refer to AS/NZS 60079.10.1.

The typographical error is highlighted in bold above; the text should read distance L and not radius r. The radius r is the vent terminal radius while L is diameter (distance) of the exclusion zone.

Distance L is measured from the centre of the vent terminal discharge point and forms the radius of the exclusion zone, in effect a sphere of exclusion with a radius L.

Revised description

In the revised description of the vent terminal exclusion zone two new figures (Figure 5.3a–Plan view and Figure 5.3b–Side elevation) will be used to explain the exclusion zone requirements and will replace the existing Figure 5.3.

Part (c) of clause 5.11.5.9 Vent terminal location will now read:

A vent terminal shall be located where gas discharge will dissipate without entering buildings or creating any hazard. The point of discharge shall-

(c) in cases where there is any object (e.g. wall, ground, etc.) in the direction of discharge and within the exclusion zone of Figure 5.3a and Figure 5.3b, be located such that there is a clearance of at least distance L to any ignition source or opening into a building in all directions.

Figure 5.3a

Figure 5.3a

 

Figure 5.3b

Figure 5.3b

To calculate L in metres:

  1. For vent terminal diameters ≤ 50 mm then L= 1.5 m
  2. For vent terminal diameters > 50 mm then L= 1.5T where T = (vent terminal diameter) / 50
  3. The exclusion zone (described above) only applies up to 200 kPa. Refer to AS/NZS 60079.10.1 for pressures exceeding 200 kPa.

For further information please contact the Gas Safety Technical Information Line on 1800 652 563.