Void Detection in a sprinklered hospital

[BCO]

Currently considering a void risk assessment that concludes that detection is not required in voids that contain only items permitted by HTM i.e.

One of the specific areas from which automatic smoke/fire detectors can be omitted with appropriate risk assessment according to paragraph 4.6 of HTM 05-03 part B, is;
 
Voids and roof spaces, of any depth, that contain only;
a)   mineral insulated wiring or wiring laid on metal trays or in metal conduits; and/or
b)   Non-combustible pipes and ductwork.
c)   Metal or plastic pipes used for water supply or drainage.[/i]

Item 2 states non combustible pipes.

A question has arisen as to whether this also includes copper pipes that carry oxygen. 

In other words if a void only contained items 1/3 above HTM appears to say no detection required (subject to risk assessment), copper pipes carrying oxygen and possibly other gas appear to fall in to item 2 and therefore would appear to comply with HTM (i.e. detection not required). Is this correct.

It’s a new hospital that is fully sprinklered (except in the voids). The proposal is not ho have detection in any void that contains only those items listed above. Where fan coil units, pneumatic pipes, fans etc are present detection will be provided. These are very few and far between therefore the vast majority of voids will not have detection.

Any thoughts greatly appreciated.

[nearlythere]

Currently considering a void risk assessment that concludes that detection is not required in voids that contain only items permitted by HTM i.e.

One of the specific areas from which automatic smoke/fire detectors can be omitted with appropriate risk assessment according to paragraph 4.6 of HTM 05-03 part B, is;
 
Voids and roof spaces, of any depth, that contain only;
a)   mineral insulated wiring or wiring laid on metal trays or in metal conduits; and/or
b)   Non-combustible pipes and ductwork.
c)   Metal or plastic pipes used for water supply or drainage.[/i]

Item 2 states non combustible pipes.

A question has arisen as to whether this also includes copper pipes that carry oxygen. 

In other words if a void only contained items 1/3 above HTM appears to say no detection required (subject to risk assessment), copper pipes carrying oxygen and possibly other gas appear to fall in to item 2 and therefore would appear to comply with HTM (i.e. detection not required). Is this correct.

It’s a new hospital that is fully sprinklered (except in the voids). The proposal is not ho have detection in any void that contains only those items listed above. Where fan coil units, pneumatic pipes, fans etc are present detection will be provided. These are very few and far between therefore the vast majority of voids will not have detection.

Any thoughts greatly appreciated.

Seems to be the case if read literally. Can't check at the minute as I am backing up but, if your text is correct, the "; and/or" bit at the end of a) is a bit confusing.
Why the "and/or"?

[Phoenix]

If there is no possibility of a fire occurring in a space then detection there would be redundant and it can be omitted.  I think your case falls into this category. 

The fact that the pipes carry oxygen is of limited significance.  Detection is put in voids to pick up incipient fires before they become noticable (by under ceiling detector or by person) outside the void and any incipient fire is not likely to cause damage to the pipes carrying the oxygen.  The typical incipient fire would be overheating light fittings or electrical equipment which is likely to emit quantities of smoke before flaming combustion begins.  Usually, such incidents are detected outside the void anyway by detectors under the ceiling or, more likely, by the noses of people.

A scenario where detection might be of benefit would be where there was a leak of oxygen and where the resultant oxygen rich atmosphere made what was previously a material of limited combustibility, within the void, into a readily combustible material AND where there just happened to be an ignition source waiting around for something to set fire to.  An improbable set of events, but, even if they do all occur together, what will the time difference be between a void detector picking up the fire and a detector below the ceiling picking up the fire?  It will be small because the fire in the oxygen rich atmosphere is going to grow rapidly.

Make sure the cavity barriers are sound and installed within the laid down distance limitations.  You say that areas containing electrical items are covered by detection anyway - this is good as they will offer the only feasible potential ignition sources.

The only other thing to be wary of is the future.  Over the years there is a very distinct possibility that combustible items and further ignition sources will find their way into the void.  Any such introduction should be accompanied by automatic fire detection - and possibly also sprinkler protection.  The only way of ensuring that this detection installation happens is to get an appropriate policy written into the fire strategy of the building.

I've done some probabilistic risk assessment work in this area and the results show that there is little return on the sizable investment of installing void detection in voids that really have a very small probability of a fire occurring in them. 

Stu

[Colin Newman]

BCO, your interpretation is correct.

Durig the drafting opf HTM 05-03 part B, the ommision of void detection described in the earlier edition of HTM 82 was modified to reflect the descriptions that were first published in the Scottish version (SHTM 82) and reflect the changes in water supply pipework.

The intention was that if only the items listed were included in a void there would be minimal ignition sources and a minimal fire load hence the most likely occurrence of a fire would be in the accommodation beneath the ceiling which should be detected by the detection present in the accommodation space.

I am aware of a different opinion that was applied in Scotland if you need details email me , but in England, your interpretation is correct.