Sirens, Sounders and Strobes - Standards for fire alarm devices

Introduction

It is perhaps surprising that, although the first British Standard for heat sensitive detectors for automatic fire alarm systems in buildings was published in 1959, the first British standard for the audible fire alarm devices (i.e. sounders), for the same systems, was only recently published, in 2001. There is still no standard for visual alarm devices although work is now progressing on this subject. Hence, fire alarm devices on the UK market have been largely unregulated, only needing to meet a few performance requirements implied by the installation code of practice BS 5839-1.

However, the European Commission's Construction Products Directive (CPD) covers the components of fire detection and fire alarm systems, including audible and visual alarm devices. This requires that, once an appropriate harmonised standard becomes available, all such components have to be certified in accordance with the standard and bear CE marking.

EN 54: Part 3

The standard for sounders mentioned above is BS EN 54-3, which is the British Standard version of the European Standard EN 54-3 and the harmonisation process for this standard is now well advanced. In fact the infamous "Annex ZA", which is required for the standard to be harmonised, recently received a positive vote in the CEN voting procedure.

The consequences of this are that all sounders falling within the scope of the standard, and placed on the market in Europe, will soon have to be certified in accordance with the standard by an appropriate notified body.

Therefore, it is a good time to review the contents of this standard and to discuss the consequences of its publication.

Scope

I think it is useful to start by looking at precisely, what is, and what is not, covered by the scope of the standard:

Hence the standard applies to the vast majority of bells, sirens and electronic sounders commonly used as fire alarm devices, including sounder bases and loop powered sounders.

What sound is required ?

Although it may appear that such a standard should specify the precise sound signals to be made by the sounders, this has not been possible. For the time being, it seems that it is not even possible to agree a specified evacuation signal throughout Europe. The standard does not therefore specify the signal but allows this to be defined by the manufacturer. It does, however, require the manufacturer to declare the main sound frequencies, frequency ranges and sound patterns, so that specifiers can choose appropriate devices from the manufacturers data.

It is also recognised that sounders with quite different sound output levels are required. For instance, in some applications it may be necessary to cover a large area with a single sounder giving a high output level, whereas in others it may be better to provide a larger number of sounders with lower output levels. The standard does not, therefore, specify specific sound output levels but requires that manufacturers declare these levels and it defines how these levels should be declared. This is intended to allow the declared specification to be confirmed during the testing, to ensure that sufficient data is provided for the system designers to determine the requirements for a particular installation and to allow meaningful comparison between products from different manufacturers.

Sound level specification and measurement

The standard requires the manufacturer to specify the minimum sound level, under anechoic/free-field conditions, 1 metre from the device at 30° intervals, in both the horizontal and vertical planes. For surface mounted (e.g. wall mounted) devices, this is required at angles between 15° and 165° to the surface, and for pole mounted devices it is required through the full 360° .

In order to relate the sound levels to human sound perception, they are recorded as an A-weighted value (dB(A)) and, for fluctuating signals, the value recorded is the maximum value measured during a complete cycle of the sound pattern with the meter set to the F (Fast) detector characteristic.

To reduce measurement errors, such as those introduced by the determination of the reference point, the measurements are made at a 3 m distance, but to conform with common practice the this is converted to a value at 1 m for the specification.

These measurements are made at the maximum and minimum of the supply voltages range(s) specified for each mode or tone provided by the device.

It should be noted that this is considerably more data than is generally given in current specifications, which often only give a value for the sound level 1 metre directly in front of the device. For modern programmable devices with many modes, and often two supply voltage ranges, this can be a significant amount of data.

The sound level measured at each of the specified angles must not be less than that specified by the manufacturer and for any angle the difference between the level measured at the maximum and minimum supply voltages must be less than 6 dB.

In the draft for comment, no absolute limits were specified for these levels. However, a number of comments were received requesting that at least absolute minimum and maximum levels are specified. A minimum level of 65 dB(A) in at least one direction has therefore been included, as this appeared to satisfy most European application guidelines, and a maximum level of 120 dB(A) in any direction was included to reduce the possibility of permanent hearing damage.

 

 

Constructional requirements

 

The standard includes a number of requirements on the construction of the audible alarm devices:

Marking and data

 

The marking requirements are similar to other components of fire detection and fire alarm systems. The marking on the device must include the following:

It is also required that the device is supplied with sufficient data for its correct usage and, as indicated earlier, this data must include the specified sound level and directional data for the device and the main sound frequencies and the frequency and temporal pattern of the sound signal.

Comparative sound level measurements

Free-field/anechoic measurements, as described above, are required to check that the manufacturer's specification for the sound output is met. However, during the other testing in the standard it is necessary to make many measurements, which are only used as relative measurements (e.g. to determine the reproducibility of the sound level from one specimen to another and the stability of specimens under different conditions). For these measurements, it is expensive and unnecessary to repeat the full free-field measurements and the standard therefore introduces a smaller scale measurement procedure in a reverberant chamber, to make comparative sound output measurements.

Durability

The standard includes a durability test to ensure that the sound out put level does not deteriorate significantly after prolonged operation. For this, the sound output level is measured by the comparative method. The specimen is then subjected 100 times to a 1 hour ON: 1 hour OFF durability cycle. During the ON period the specimen is supplied with the maximum specified supply parameters in the mode of operation which consumes the most power. After the 100 cycles the sound output is measured again and must not have reduced by more than 6 dB.

Environmental tests

The environmental test schedule for the audible alarm devices is taken from the CEN Catalogue of environmental tests and incorporates severities for both indoor (Type A) and outdoor (Type B) devices. The severities for these tests are summarised in the following tables:

Climatic Tests

TEST

Severity

 

Type A (indoor)

Type B (outdoor)

Dry heat (operational)

Temperature: 55° C

Duration: 16 h

Temperature: 70° C

Duration: 16 h

Dry heat (endurance)

No test

Temperature: 70° C

Duration: 21 days

Cold (operational)

Temperature: -10° C

Duration: 16 h

Temperature: -25° C

Duration: 16 h

Damp heat, cyclic (operational)

Lower temp: 25° C, >95%RH

Upper temp: 40° C, 93%RH

Cycles: 2

Lower temp: 25° C, >95%RH

Upper temp: 55° C, 93%RH

Cycles: 2

Damp heat, steady state (endurance)

Temperature: 40° C

Humidity: 93%RH

Duration: 21 days

Temperature: 40° C

Humidity: 93%RH

Duration: 21 days

Damp heat, cyclic (endurance)

No test

Lower temp: 25° C, >95%RH

Upper temp: 40° C, 93%RH

Cycles: 6

SO2 Corrosion (endurance)

Temperature: 25° C

Humidity: 93%RH

SO2 conc: 25 ppm

Duration: 21 days

Temperature: 25° C

Humidity: 93%RH

SO2 conc: 25 ppm

Duration: 21 days

Water ingress

IPX1 (Vertical dripping)

IPX3 (Spray to 60° from the vertical)

 

 

Mechanical Tests

TEST

Severity

 

Type A (indoor)

Type B (outdoor)

Shock (operational)

Pulse: Half sine

Duration: 6 ms

Acceleration: (1000-20M)ms-2, For mass M £ 4.75 kg

No test for mass M > 4.75 kg

No. pulses: 3 in each of 6 directions

Impact (operational)

Impact Energy: 0.5 J

No. Impacts: 3

Vibration (operational)

Frequency range: 10 to 150 Hz

Acceleration: 5 ms-2

Sweep rate: 1 octave/min

No. axes: 3

No. Sweep cycles: 2/axis/functional condition

Vibration (endurance)

Frequency range: 10 to 150 Hz

Acceleration: 10 ms-2

Sweep rate: 1 octave/min

No. axes: 3

No. Sweep cycles: 20/axis

Mechanical ingress

IP2XC

IP3XC

 

The device shall be subjected to the following electromagnetic compatibility immunity tests as described in EN 50130-4: 1995. These tests shall all be applied in the quiescent state and the radiated and conducted RF tests shall also be applied while the device is sounding.

Electromagnetic compatibility Tests - EN 50130-4

Port

Environmental

Phenomena

Severity
(Types A and B)

Basic Std.

Enclosure

Radiated RF

80 to 1000 MHz

10 V/m

80% AM (1 kHz sin.) &

1 Hz Pulse mod.

IEC 1000-4-3

EN 61000-4-3

Electrostatic

Discharge

6 kV contact discharge

8 kV air discharge

IEC 1000-4-2

EN 61000-4-2

DC, low voltage & Signal lines

Voltage variations

Conducted RF

0.15 - 100 MHz

10 V (140 dBm V)

80% AM (1 kHz sin.) &

1 Hz Pulse mod.

ENV 50141

Fast transients

1 kV (peak)

5/50 ns Tr/Th pulses

5 kHz Rep. frequency

IEC 1000-4-4

EN 61000-4-4

High energy voltage surge

1 kV line-to-ground**

1.2/50 m s Tr/Th pulses

IEC 1000-4-5

EN 61000-4-5

* Via 10 Ohm series resistor. ** Via 40 Ohm series resistor.

Included in the sound level measurements.

Voice Sounders

As hinted in the discussion of the scope of EN 54-3, it is not clear if "voice sounders" are really included in or excluded from the scope. Generally voice sounders have a message broadcast sequence similar to that specified in BS 5839-8 for voice alarm systems. This consists of an attention drawing signal/tone followed by a pre-recorded voice message. If the voice message is considered to be the primary signal then the devices are excluded. However, if the tone is considered to be the primary signal and device is considered to be a "voice enhanced sounder", as they are sometimes called, then they are included.

I am sure that it was not originally intended to include these devices in EN 54-3 and the problem with including them is that there are no requirements for the voice message or the broadcast sequence. The CEN working group responsible for alarm devices is currently considering how to deal with voice sounders. The group is considering what additional requirements are necessary but it is not yet decided if these will be included into an amended EN 54-3 or into a separate standard.

One point that has become clear is that if voice sounders are operating in close proximity, it will be necessary to synchronise their operation, if the voice message is to be intelligible. Requirements for this synchronisation are currently being drafted and it is proposed to add these to the standard as an option with requirements.

Visual fire alarm devices (e.g. strobes / flashing beacons etc.)

There is currently no British or European standard for visual fire alarm devices. However the same CEN working group is preparing a first draft based on EN 54-3 but with optical measurements replacing the various acoustic measurements.

It is likely that, for strobes using xenon flash tubes, the measurement of the performance of the flashing light will be based on the Blondel-Rey law and will therefore be somewhat similar to the method used in UL 1638 and UL 1971. However, it appears that other techniques may be required for devices with longer duration flashes.

It is also clear that where a number of devices may be in view at the same time there could be requirements to ensure that the flashes are synchronised. It is therefore also intended to add this as an option with requirements, as for voice sounders.