Decibel Level

[AM]

Is there a 'rule of thumb' to estimate the sound level of a fire alarm as it passes through a fire door? If a fire alarm sounder is placed in the common area of a block of flats, and it has to pass through a fire door and a bedroom door, is it likely that the sound level would be sufficient at the bedhead or would sounders be required in each individual flat?

Thanks in advance.

[John Dragon]

Rule of thumb is "You need a sounder in any bedroom". plus adequate sound levels in other rooms (65 decibels)

In flats this usually equates to a sounder in each bedroom plus at least one more in hall and / or lounge depending on layout.

A bell / sounder generally outputs about 93 decibels and a good fire door will stop 30 of them.

It is very common for sparkies to just install one sounder in the hall (often as per plans given to them) - This usually does not comply.

[Allen Higginson]

I thought it was 10dB drop off through a fire door and 6 dB at 2 metres away (another 6 at 4 metres and another 6 at 8 metres etc.)?
Regardless,getting 85dB at the bedhead using a sounder outside the door is going to take something that causes blood to come from your ears though.

[The Colonel]

I usally work on 20db per door and when it comes to flats, bedsits etc a sounder in the common area is rarely sufficent to give sufficent db at the head of the bed. Usually 75db

In one case whilst a Fire Safety Officer we found that less than 45db were recorded at the bed head after passing through two doors in flats for young people, extra sounders were required before residents were allowed into the flats/bedsits. Bit of a race for the sparks before the local Bishop performed the opening 3 days after the tests. Was also an eye opener for the local building control officer who wasnt that good with the alarm side of things.

[Graeme]

Is there a 'rule of thumb' to estimate the sound level of a fire alarm as it passes through a fire door? If a fire alarm sounder is placed in the common area of a block of flats, and it has to pass through a fire door and a bedroom door, is it likely that the sound level would be sufficient at the bedhead or would sounders be required in each individual flat?

Thanks in advance.

drop 20dba through a normal door 30 for a fire door.

the sound drops by 6dba every time the distance from the sounder doubles.

the sound is calculated first at 1m from sounder.

deduct 3dBA for safety tollerance and deduct another 3 dBA for manufacurer tollerance.

if you come to a door you don't measure the distance from sounder through the door and then to the bed,it's work out sound at door,then from other side of door.

so
say you had a sounder at 105 dBA in a corridor 7m from a door (7m=17dBa drop)

105-17=88
88-3(safety factor) then -3 (manufacturer) =82

82 at door then -30 for a fire door

=52 dBA at other side of door

then say 5m to bed  52-14 =38dBA at bed head

easy answer

sounder in every room above near the bed

[John Dragon]

I thought it was 10dB drop off through a fire door and 6 dB at 2 metres away (another 6 at 4 metres and another 6 at 8 metres etc.)?
Regardless,getting 85dB at the bedhead using a sounder outside the door is going to take something that causes blood to come from your ears though.

75 dB at the bedhead!!!

[Allen Higginson]

I thought it was 10dB drop off through a fire door and 6 dB at 2 metres away (another 6 at 4 metres and another 6 at 8 metres etc.)?
Regardless,getting 85dB at the bedhead using a sounder outside the door is going to take something that causes blood to come from your ears though.

75 dB at the bedhead!!!

Just checking (and to be pedantic I didn't say I was quoting the BS in reference to 85dB,only making a general statement....lol)!!!

[kurnal]

If these are flats, if they are constructed to building regs standards ie full compartmentation,  we dont need an alarm in the common areas and we would install a part 6 system in the flats.

BS5839 Part 6 allows relaxations on sound levels and indicates that 75db at the bedhead may be relaxed (apart from Grade A systems in large buildings)

[monkeh]

quick question.

in the flats where my girlfrind was living last year, there was a gent vigilon system in aql the communal areas, a single heat detector in each flat hall, then a mains smoke detector in each bedroom and mains head detector in the kitchen/living room.

problem was the closest sounder was in the external hallway outside the flat, and it was only the integrated optical/heat sounder type that gives off very little noise.  you could barely hear the thing in the rooms when it went off and only then when you knew it was coming and could listen for it.  

surely if there's a complete fire alarm system in a building, then ALL areas have to meet the required dB levels, even though the rooms themselves are only covered by mains detectors?

i was going to pull them on it apart from the fact that i only noticed it about 2 weeks before she was due to leave when i was there while they were testing.

[kurnal]

I suppose there are two opposite arguments here.
If a system is installed in the common areas for life safety  then it should conform to the BS5839 part 1 and this includes sound levels.

But did it need such a system at all?
If the compartmentation is in place there is no reason to install a life safety system in the common areas. It could be appropriate to install a P system  to alert the building managers or call centre, and not to install any sounders?

[Davo]

Chaps
As a H & S officer (though most of my time is Fire RAs etc), if the sounder is 105dB at one metre, then I can tell you it will be 102dB at 2 metres, 99 dB at 4 metres etc, ie double the distance equals a 3dB drop. This is where there is no attenuation by objects such as walls, doors etc.

Never mind tolerances, each installation should be certified before handing over. If in any doubt about an older installation, measure the noise at the bedhead.
(How do you know what the walls are constructed of? Different thicknesses of breeze block and indeed different types of breeze block have vastly different impacts on noise levels. So does the frequency level of the sounder.

[Crusader]

Not quite a rule of thumb, but there is a method to calculate attenuation of sound pressure levels in The SFPE Handbook of Fire Protection Engineering, 3rd Edition (see, Schifiliti et al, Design of Detection Systems, Section 4, Chapter 1, pp 32-39). The method deals with the effects of partitions, doors, surface finishes, frequency of sounder, etc. Having played with this method using a spreadsheet, I agree that you will probably need a sounder in every bedroom, otherwise the maximum sound pressure level allowable is likely to be exceeded from sounders in the corridor alone.

[Dinnertime Dave]

All seems very complicated to me, after sitting in a classroom at FSC and working everything out using a calculator, we then set an alarm off and walked through doors until you couldn’t hear it. The result was -

Go through 2 doors you can’t hear the alarm. Each door or wall takes between 15-20 dB off a 105dB alarm. Every bedroom will require a sounder.

[Graeme]

Chaps
As a H & S officer (though most of my time is Fire RAs etc), if the sounder is 105dB at one metre, then I can tell you it will be 102dB at 2 metres, 99 dB at 4 metres etc, ie double the distance equals a 3dB drop. This is where there is no attenuation by objects such as walls, doors etc.

Never mind tolerances, each installation should be certified before handing over. If in any doubt about an older installation, measure the noise at the bedhead.
(How do you know what the walls are constructed of? Different thicknesses of breeze block and indeed different types of breeze block have vastly different impacts on noise levels. So does the frequency level of the sounder.

well all the training i have had must all have been wrong then.

[Martin Burford]

I have been following this topic for a while and cannot for the life of me understand why thickness of walls, doors or anything else is relevant. What is, is that 75db is reached at the bedhead.........If it cannot be then steps need to be taken to remedy this by the installing engineer. all this should be confirmed during the verification process.
For god's sake keep these issues simple.
Conqueror