Audibility in flats

[David Rooney]

6 storey property deemed unfit for a stay put policy by the powers that be with over 40 apartments is now required to extend the fire alarm system into the privately owned flats.

75db at the bed head has been specified by the fire officer .....

In view of pt 6 allowing 85db at the bedroom door is this reasonable or correct ?

Thanks

[kurnal]

Hi David its good to hear from you again.
It is difficult to speculate on why a full evacuation strategy has been determined as a suitable strategy in this case and the reasons behind it. One must trust it has been properly thought through as the best solution. The extent of the detection is not specified.

However my gut feeling is that it is wrong to mix and match standards in this way. I would argue that Part 6 systems were designed for use in specific domestic situations and are really only  appropriate for individual dwellings though this is then stretched to cover some smaller HMOs. I would speculate that part 6  was probably a compromise,  written around the best available sounder technology and what could be driven by a small battery supply.
It would not make it appropriate to extend the standard acceptable in a small individual dwelling to a completely different scenario, with far greater potential for persons to get hurt if something goes wrong.   

If the alarm is needed because people are likely to get hurt if they dont leave the building then it should conform fully to the part 1 standard in my opinion.

[David Rooney]

Hello Kurnal

I'm never far away !

Long story short, the detection is L3 with a heat detector only inside each flat, the escape routes are covered and alarm levels in the escape routes are fine as this was designed as a stay put strategy (by others I might add).

Suffice to say the men in black have now decided the place must be a one out all out due to compartmentation issues.

We have nothing to do with the design but I'm interested to know why the 85db in the flats can't be applied? Regardless of the size and complexity of the building each flat is a flat and if it were a new build and smoke alarms were fitted then 85 would be acceptable.

So why could 85db at the bedroom door not be acceptable from the house system?

I've seen lots of similar properties with a detector/sounder in the lobby to the flat, never with sounders in every bedroom .....

[kurnal]

I might well agree with you Dave if I came across it too.
I suppose it depends on what the compartmentation issues are- where the problems lie. If as an extreme you have six storeys of flats over each other with no compartmentation between the floors and for example unprotected ventilation shafts then I would want to make absolutely certain that in the event of a fire in the ground floor flat the people on the top 4 floors were alerted as quickly and reliably as possible bearing in mind they are reliant on the heat detector in the flat lobby in the flat on fire.  If we require to wake people from sleep as a result of a fire elsewhere in the building and if a part 1 system is appropriate then we  should work to the 75db at the bedhead standard as a benchmark.

Having said that I would much rather work on improving the compartmentation to support stay put!

But I could also think of many other practical situations in which I would accept the L3 system and a variation in respect of sound levels. If I came across a system with a detector sounder in the lobby I would be unlikely to ask for it to be retrospectively upgraded, but if designing a new system as a compensatory feature I would design to part 1.

[David Rooney]

Thanks Mr K .....

Thought provoking as ever 

I'm not privvy the "issues" but as you allude to, if you're that worried about the alarm levels and the compartmentation is that bad then I suppose it should equally justify installing detectors within the flats on the house system as well.... which would be a nightmare !

Apart from none of the residents wanting the detectors or to pay for them, we are back to the "what happens when you burn the toast" scenario .....

Tis a bit of a nightmare ......

[colin todd]

So, Big Al, let me see if I am understanding your always irrefutable and sound logic right. People have a fire in their own flat, which surely is an immediate threat to them big time, but there is a fire elsewhere in the block that might just happen to threaten them, but might not, so the sound pressure level to rouse them from sleep has to be such that the alarm is more than twice as loud?

Yep, makes perfect sense I am sure, I just am missing something critical.

[kurnal]

Yes Colin I agree.

So what is your helpful advice for the OP?

Dave you are right, one out all out strategies don't work, wont work and never will in flats. Such a strategy should always be the  last resort if all else has failed.  

[colin todd]

You agree with what? And what is an OP. (I know the police use the term as an observation point).

[kurnal]

An Original Poster. It is an oft used abbreviation by regular forum users.

I agree that prima facie persons are likely to be in greater immediate danger from an alarm originating in their own flat.

If I recall someone wrote a standard for domestic life safety fire alarm systems and a different standard for other fire alarm systems covering other types of premises.

 We are of course used to the concept of mixed systems but that was not the original question. It subsequently became apparent that this was an existing system under discussion and not a new design.

Do you have any practical advice in response to the original question? 

[Bill J]

Hi David,

Not wanting to stand in the way of the resident experts, who both have valid points, and have both helped me out in the past.....

We often come across this in Central London, and often we never get to see the inside of any apartments. It came from an old Westminster Council Guide and probably ecisted before that, and we still (when asked) install the same, we make ot very clear that we have not allowed for 75db at the bedheads of the bedrooms, but have allowed for a combined sounder/detector adjacent to the front door to provide a means of detection within the flat before the door is breached, and a means of alarm within the flat to indicate an external fire. We then provide an additional cost for any extra sounders where a second floor is in place or where there is an additional door between any bedroom and the front door.

This we ALWAYS state should be in addition to the homeowner/tenant/occupier etc providing their own internal part 6 system. Part 6 states there  appears to be no evidence to show that lives are being lost due to inadequate audibility of the fire alarm signal from smoke alarms, except where people are incapacitated to such a degree that even much higher sound levels would not waken them. This might be because, in their own homes, people can be roused by an unusual sound of relatively low level compared with the sound level that may be required to wake them in premises with which they are unfamiliar (e.g. a hotel).

If we all agree on this then it is put onto a part 1 certificate as an agreed variation. If preferred than it really is a sounder into each sleeping space, which will be additional cost and disruption to the aesthetics.

There isnt a one size fits all solution that i am aware of....but happy to be corrected, and always willing to learn!

Bill

[kurnal]

Thanks Bill thats exactly the type of helpful response that made has firenet such a valuable resource in the  past.

I hear tales that such a arrangement is common in London even in premises with a stay put strategy?

Yes part 6 does include the "no bodies on the streets" argument and it is a valid point. It might also be argued that perhaps 75dbA at the bedhead is more than is necessary to wake most people. After all alarm clocks are in the business of waking people up and very few on the market deliver 75dbA. It would be interesting to know the background to the range of sound pressure levels recommended in Part 1. 

Having said that the bottom line for me is that if a system is to be installed then it must be fit for purpose. In a building with a stay put strategy there should be no need for an alarm in the communal areas. Where one is installed  it is because a stay put strategy is inappropriate for that particular building and there is no practicable  alternative. Often a heat detector sounder combination in each flat lobby will be sufficient but often in these buildings internal flat layouts and travel distances are such as to make this inappropriate. We regularly come across sounders in the common areas only.

[Midland Retty]

oooo hang on a minute.... owner/occupiers fair enough... but you expect tenants to install part 6 systems?. Sorry not sure that is particularly right... sorry Kurnal would you like to thank me for bringing this up?....apparently you take me for granted, so.....

[AnthonyB]

Audibility is only half the issue, detector provision in relation to the structure surely is the other. A heat in the lobby is little use if the fire has breached the floor above the room of origin or a shaft adjacent to the RoO because the compartmentation is so poor in these areas, the doors aren't the only vulnerability. In fact I recall one site where the internal doors would still be standing long after the ceiling failed and they had gone for smoke heads with loop sounder bases off the common system throughout each flat to compensate (all done well before the RRO was even a gleam in the lawmakers eye).

Unless you are party to all the relevant information it's difficult for you to comment.

[kurnal]

The following is taken from BS5839-6

13.1.2 Audibility
A fire detection and fire alarm system only provides satisfactory protection of life if it is capable of rousing the principal occupants of the dwelling from sleep (e.g. the adult occupants in a typical single-family dwelling). No particular sound pressure level is certain to rouse all occupants of a dwelling in all circumstances. Depth of sleep varies during the course of the sleep period and also varies from one person to another. Greater sound pressure levels are often required to rouse children from sleep than are necessary in the case of adults. BS 5839-1 recommends that, if an audible alarm is intended to rouse sleeping persons, a sound level of 75 dB(A) should be achieved at the bedhead when all doors are shut, although this will not guarantee that every person will be awakened, particularly if they are under the influence of alcohol or drugs.

Most fire detection and fire alarm systems in dwellings comprise smoke alarms, which are usually fitted in, at least, the circulation areas, such as hallways and landings. BS 5446-1:2000 requires that the sound output of a smoke alarm be at least 85 dB(A) at three metres. Most domestic doors attenuate sound by around 20 dB; greater attenuation can occur in the case of solid doors, such as fire doors. It is therefore unlikely that a smoke alarm on, for example, the upstairs landing of a two-storey house will produce a sound level of 75 dB(A) at the bedhead in each bedroom, particularly if the bedroom doors are shut; levels of 55 dB(A) to 65 dB(A) are more likely. There appears to be no evidence to show that lives are being lost due to inadequate audibility of the fire alarm signal from smoke alarms, except where people are incapacitated to such a degree that even much higher sound levels would not waken them. This might be because, in their own homes, people can be roused by an unusual sound of relatively low level compared with the sound level that may be required to wake them in premises with which they are unfamiliar (e.g. a hotel).

As far as I can see the last sentence of the commentary is not based on any research though I would be pleased to be corrected.

It is widely taken as custom and practice by many alarm engineers and most electricians  that in a mixed system, if 85db at the bedroom door measured with the door ajar  is good enough to wake you in your own home then the same alarm level is all that is required from the pt 1 communal system.  

The crux is whether this should be viewed differently when there is a duty of care toward the occupants of the dwelling.


Oh and I am grateful to my honorable colleague monsignor martian for his valued contribution.

[Graeme]

I have been asked to install a part 1 system within the common areas to L2 but no afd or sounders in the flats.

Looking at the area i doubt the system will outlast the panels stand by duration.