Image courtesy of Standards Australia
We all have rules of thumb we follow. Whether it’s an urban myth that works or the advice of someone we trust. Whether it’s an unusual project or we are just having an off day – sometimes we question these rules of thumb. Joe Zita, an associate of ours at Approval Systems mentioned to Building Design Compliance this issue. Joe was on the money from the outset, but it took a couple of run throughs of the standard before we were convinced.
The “urban myth” that you can only provide external hydrant coverage to one level above the access level (typically the ground level) comes from this diagram above (Fig 3.2.2.2) from AS2419.1-2005. The note to the diagram only serves to reinforce the “urban myth”. It says “Due to difficulties associated with fighting building fires, internal fire hydrants are required in fire-isolated stairs for levels more than one floor below ground and one or more levels above ground.”
Our understanding of the notes to these diagrams is that they provide guidance and are informative only. The must is in the text which says:“external hydrants may be used to protect portions of a building up to one level level below and levels above the access level, subject to the limitations defined in Clause 3.2.1.”
In summary, 3.2.1 talks about the route of the hose being the most direct, including along the nosings of the stairs, except for in the stair enclosure where it must be measured to the outer perimeter.
From closer review of the notes on the diagram above we note the use of the word “may” for internal hydrants at more than one level above the access level. By comparison for the level(s) below the access level it says “internal hydrant required on this storey” whereas above the access level it says “Internal hydrants may be required on these stories.”
The diagram is also limited in its application to buildings with fire-isolated stairs e.g. residential buildings with a lower carpark level can have an open stair with up to 3 residential levels above or with sprinklers they can have four levels above. Commercial buildings with sprinklers can have up to 3 levels with an open stair. These examples hilight some of the limitations in the application of Figure 3.2.2.2.
Tags: BCA, Buiding Permits, Building Regulations, Fire Hydrants
The above comments concludes that a hydrant system can be designed so that more than 1 level above ground can be covered as long as fire isolated stairs are not provided.
This maybe a desirable outcome as the pressure required for an external hydrant is only 200 kPa were an internal is 350 kPa plus the static pressure due to the height of the building. Many town main water supplies are unable to provide the pressure to the internal hydrant and hence will be forced to use a pump at great expense to the developpment.