Fire Section

The minimum sound levels must be produced in all parts of the building, where any person may be working. This includes restricted area's that are infrequently visited, such as service ducts, or lift shaft motor rooms.

Life Protecting
As audible alarms are essential for the protection of life, a minimum of two independent sounder circuits must be provided to guard against failure of one, even if the sound level can be achieved with just one sounder.

Property Protection
In Type P systems the minimum sound levels must be produced in the areas required to summon fire fighting assistance. A sounder should also be provided close to the control and indicating equipment and there should be one outside to direct services to the correct entrance.

In practice most fire detection and alarm systems involve both property and life protection. Most systems should therefore meet all the above requirements.

In general fire alarm sounders must not be used for any other purpose, with the established exception of class changes in school where coded signals of not more than five seconds duration can be used. Public address equipment can be used to give warning of fire subject to certain conditions. Visual alarm signals should be considered to complement alarm sounders where there is a high level of noise or the occupants may be hearing impaired.

Sound Output
All sounders in a building should be of similar type, do not mix electronic sounders with bells.

As a general rule of thumb, the sound level will reduce by 6dB every time the distance from the sounder is doubled, starting from 1m from the sounder. Sound levels are normally quoted on-axis, i.e. directly in-line with the middle of the sounder. This is normally the loudest position. In order to assess the sound level at any particular point it is necessary to allow for the distance from the sounder and the angle off-axis, as head height varies with size of person.

Sounders should produce:

m+s	Sounder Output at 1 meter dB(A)
1	65	70	75	80	85	90	92	94	96	98	100	102	104	106	108	110	112	114	116	118	120
2	59	64	69	74	79	84	86	88	90	92	94	96	98	100	102	104	106	108	110	112	114
3	55	60	65	70	75	80	82	84	86	88	90	92	94	96	98	100	102	104	106	108	110
5	51	56	61	66	71	76	78	80	82	84	86	88	90	92	94	96	98	100	102	104	106
10	45	50	55	60	65	70	72	74	76	78	80	82	84	86	88	90	92	94	96	98	100
20	39	44	49	54	59	64	66	68	70	72	74	76	78	80	82	84	86	88	90	92	94
30	35	40	45	50	55	60	62	64	66	68	70	72	74	76	78	80	82	84	86	88	90
50	=	36	41	46	51	56	58	60	62	64	66	68	70	72	74	76	78	80	82	84	86
100		=	=	40	45	50	52	54	56	58	60	62	64	66	68	70	72	74	76	78	80

Recommended Minimum Sounder Level at the bed head is 75 dB(A) and is shown in the red boxed text.

m+s	Sounder Output at 1 meter dB(A)
1	65	70	75	80	85	90	92	94	96	98	100	102	104	106	108	110	112	114	116	118	120
2	59	64	69	74	79	84	86	88	90	92	94	96	98	100	102	104	106	108	110	112	114
3	55	60	65	70	75	80	82	84	86	88	90	92	94	96	98	100	102	104	106	108	110
5	51	56	61	66	71	76	78	80	82	84	86	88	90	92	94	96	98	100	102	104	106
10	45	50	55	60	65	70	72	74	76	78	80	82	84	86	88	90	92	94	96	98	100
20	39	44	49	54	59	64	66	68	70	72	74	76	78	80	82	84	86	88	90	92	94
30	35	40	45	50	55	60	62	64	66	68	70	72	74	76	78	80	82	84	86	88	90
50	=	36	41	46	51	56	58	60	62	64	66	68	70	72	74	76	78	80	82	84	86
100		=	=	40	45	50	52	54	56	58	60	62	64	66	68	70	72	74	76	78	80

Recommended Minimum Sounder Level at for normal area is 65 dB(A) and is shown in the blue boxed text.

Note: The sound level near the control panel should not be so high that a telephone cannot be used to summon help from the fire brigade.

Attenuation of sounders
Fire alarm sounders may often be heard in adjacent rooms but the sound level will be attenuated by any door.

Typical attenuation figures are:

It is also important to consider the room's use. Are there any obstacles (including furniture) to the sound, and how many people will be present in the room? Both people and furnishing will attenuate the sound level.

The fire alarm sounders should be limited to below 120 dB(A), sound levels below this figure, for a short duration is unlikely to damage hearing.