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why are there differences in sound pressure levels in BS5839 PARTS 1 AND 6


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I'd like to know what everyone's thoughts are regarding why the requirement of bs5839-1 is 75dB at the bed head but 5839-6 is 85dB at the door (as is the evacuation alert standard). 

85dB at a door could easily be 55dB at the bed head with the door closed, 20db lower than what part 1 requires. I asked tom brookes owner of Zzues training who is chairman of FSA and more. He said he had tried to get them to standardise and make it the same but it fell on deaf ears. 

does anyone know the reasoning behind it? any scientific reasoning? how has someone come to the conclusion a low sound level is enough to wake you at home but in a hotel it needs to be much higher? 


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Ignore the above - here is the official rationale:

A fire detection and fire alarm system only provides satisfactory protection of life if it is capable of rousing the principal occupants of the dwellings from sleep (e.g. the
adult occupants in typical single-family dwellings). No particular sound pressure level is certain to rouse all occupants 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. Hearing loss, which can occur gradually with ageing, and alcohol intoxication also result in the need for higher sound pressure levels to rouse people from sleep. BS 5839-1 recommends that, if an audible alarm is intended to rouse sleeping persons, a sound level of 75 dB(A) ought to 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 EN 14604 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).

The historic adequacy of sound pressure levels applies to sheltered housing as well as general needs housing. However, the changing demographic of sheltered housing
residents means that the ageing population now found in sheltered housing is likely to be more prone to hearing loss than the general population. Accordingly, when a new fire detection and fire alarm system is installed in sheltered housing (either when the building is first constructed or when a replacement system is installed in existing sheltered housing), it is now considered appropriate for higher sound pressure levels to be provided in the principal bedroom of each dwelling unit than those traditionally achieved.

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@AnthonyBthanks for your reply, I wasn't sure what the other reply was getting at either. I was aware of this in BS5839-6, in my opinion though it just seems daft to not have part 1 & 6 standardised in regards to sound levels. I mean it basically says it itself to my eyes.... it states that not all sound levels is certain to wake everyone, and children and people under the influence will require greater levels, therefore in my opinion it would make so much sense to make part 6 a requirement for 75dB at the bed head. This would make the standard safer than now and would require a device in every bedroom in a domestic property. I know they say that there is no evidence to suggest lives are being lost due to this but the safer the better? also, don't know how they would even prove no lives are lost due to this?? if someone dies in a house fire, they don't know whether they just couldn't escape or never woke up in time?? its so flawed to me. Also what solid evidence is there anyway to show people wake easier in their home than a hotel? 

It doesn't sit right with me and is just my opinion but 55db when bedroom door shut is unlikely to wake those in their home when they've had good amount to drink and are knocked out big time, 85dB in the bedroom more than likely would however. 

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