scope of fire detection detailed in Lacors

[tmprojects]

firstly, i'm back! after a long absence its good to see the regulars are still here. hello to all.

but, back to business, here's my question.

in a converted Victorian town house of 5 floors. with the conversion pre-dating 1991 building regs. where Lacors applies.it requires a sounder and heat detector in each flat with FD30S doors. it also requires SD on each landing.

my question is this.

if each flat has a heat detector and sounder and a FD30S door. what is the purpose of a smoke detector on each floor?

my rationalle is this. if the FD30S door works correctly there will be no smoke leakage into the common stair thus the internal heat detector will activate first. if it fails, then the smoke will rise and a single smoke detector at the head of the stairs would be sufficient.

i cannot see the benefit of installing a smoke detector on each floor of the protected stair in this instance, wouldn't one suffice?

[nearlythere]

firstly, i'm back! after a long absence its good to see the regulars are still here. hello to all.

but, back to business, here's my question.

in a converted Victorian town house of 5 floors. with the conversion pre-dating 1991 building regs. where Lacors applies.it requires a sounder and heat detector in each flat with FD30S doors. it also requires SD on each landing.

my question is this.

if each flat has a heat detector and sounder and a FD30S door. what is the purpose of a smoke detector on each floor?

my rationalle is this. if the FD30S door works correctly there will be no smoke leakage into the common stair thus the internal heat detector will activate first. if it fails, then the smoke will rise and a single smoke detector at the head of the stairs would be sufficient.

i cannot see the benefit of installing a smoke detector on each floor of the protected stair in this instance, wouldn't one suffice?

Is it not that if a fire is confined to the flat the detection there is just to warning flat occupiers? If the fire exits the flat it sounds the detector in the common area and warns other building users?

[SamFIRT]

I investigated a fatal fire recently where the heat detector in the flat did not activate but the smoke detector in the approach corridor did and raised the alarm for the other residents. The fire was a smouldering fire caused by a faulty electrical flex fitted with an over rated fuse, finally progressing to a small flaming one. There were a lot of low temperature dense smoky gasses in the flat, which leached through the flat's entrance door sufficiently to activate the ionisation detector head in the corridor. The lady occupant of the flat was rescued by our crews but died the next day. All the other occupants of the premises were OK.

[Bill J]

As I understand it.

The Heat Detector in the flat is intended to provide protection to the common parts, and is normally part of the Common parts system, i.e. its activation will sound an alarm throughout the premises. Being a heat detector it will be unaffected by the tenants toast and cooking practices.

The Flat would normally have Smoke Alarms which are not connected to the Common parts, in order to raise awareness within the tenanted area, without disturbing the rest of the block. If the fire spreads, (e.g. tenant not at home to respond to local alarm) The Heat detector will respond at a later point.

The reason for the Smoke detector on each landing, is that it is a requirement of BS5839 part 1, (Which is what the Common parts system is based on), but also in these situations, smoke coming through a door will be cooled significantly and not raise to the head of the stairs.

This is referred to as a mixed system by BS5839 Part 6.

[Bill J]

I investigated a fatal fire recently where the heat detector in the flat did not activate but the smoke detector in the approach corridor did and raised the alarm for the other residents. The fire was a smouldering fire caused by a faulty electrical flex fitted with an over rated fuse, finally progressing to a small flaming one. There were a lot of low temperature dense smoky gasses in the flat, which leached through the flat's entrance door sufficiently to activate the ionisation detector head in the corridor. The lady occupant of the flat was rescued by our crews but died the next day. All the other occupants of the premises were OK.

I hadnt read SamFIRT's post this before I typed my response.

Very sad, but does explain the reasoning.

[Midland Retty]

Hi TM Projects - Welcome back

You raise a question which I hear commonly. On the face of it the detector in the room of fire origin should raise the alarm before smoke / flame breaches the communal area. Furthermore I hear alot of people debate the fact that if the smoke detectors in the communal area activate they only serve to warn occupants that their escape routes are essentially smoke logged and may be impassable.

Bill's response eloquently describes why we need AFD in communal areas as well as rooms directly off the communal area, and SAMs example a sad reminder that sometimes the detector in the room of fire origin doesn't activate.Atleast the detectors in the communal areas did go off to give warning to the other occupants of the building.

Also I have dealt with three instances of tenants setting fire to combustibles in the communal areas of HMOs which is another reason why AFD in the communal areas is a good idea.

[BCO]

Interesting question. Is it not the case that doors with smoke seals do allow smoke to pass? I think the accepted rate at which smoke passes (can pass before it fails the test) through a smoke sealed fire door is 3m3/m/hr. So the chance that the detector in the stair/landing won’t be activated must be very low.  Therefore for the reason illustrated above in Sam’s post detection in the common area must be a good idea

Coincidentally we have heard recently that an LA EHO inspector has been asking for smoke seals on bedroom doors (bedsit arrangement) to be removed so as to allow greater spread of smoke to the smoke detector in the stair. Is this right or am I missing something??

[lancsfirepro]

Coincidentally we have heard recently that an LA EHO inspector has been asking for smoke seals on bedroom doors (bedsit arrangement) to be removed so as to allow greater spread of smoke to the smoke detector in the stair. Is this right or am I missing something??

Then he wants a kick in the plums.  You only have intumescent strips (without smoke seals) where there is no detection in the room opening onto the escape route.  In bedsit arrangements you'd have detection in the room therefore intumescent strips with smoke seals are the order of the day.

[BCO]

Then he wants a kick in the plums. 

I tend to agree. However it’s a women! Any other suggestions.

[nearlythere]

Then he wants a kick in the plums. 

I tend to agree. However it’s a women! Any other suggestions.

Stroke the heater detectors?

[tmprojects]

Thanks for the responses.

I'm not sure I've made my point very well.

I completely agree that there should be SD in the stairwell because its likely smoke may leak into the stairwell before the HD activates thus giving sufficient early warning.

My question was. Wouldn't just one at the head of the stairs suffice? Why put a SD on each landing in a small confined stairwell you commonly find in most house conversions?

[Tom Sutton]

Does this answer your question.

In the mid 1980,s research was carried out on behalf of the Home Office by the BRE. They were contracted to carry out very elegant research work, using a full scale mock up of a corridor with rooms at Cardington. They set fires in a room and observed conditions in the corridor, with detectors 15m apart. In general, they found the set up was often ok and people were given early enough warning. However, under certain circumstances, which included no intumescent strips on the doors they could smoke log the corridor before an alarm was given.
Further research showed that this depended on the size of the gap around the door. Sods law was that a 3mm gap was worst case, and further work showed that the problem was caused not so much by the hot buoyant gases from the fire but from the pyrolysis of the timber at the head of the door, which resulted in relatively cool, heavy tarry smoke entering the corridor and not having enough buoyancy to operate detectors 15m apart.

If that was the case then the smoke is unlikely to rise to the head of the stairs and maybe fill the staircase from bottom to top?

[tmprojects]

Excellent answer Tom. Thanks

[colin todd]

Yes, Thomas an excellent answer indeed.  I seem to have read it before somewhere.......... Did you want to give an acknowledgement to the author.

[Tom Sutton]

Absolutely Colin it originated from some guy who was rabbiting on about should it be heat or smoke detectors in hotel bedrooms his initials were CT.