Although voice alarm systems have been around for some time, the development of standards to support their use as fire warnings has happened more slowly. Bernard Laluvein examines the impact of the most recent standards in improving their reliability and integrity.
When installed in a building, a voice alarm (VA) system acts as the alarm output function of the fire detection system and, as such, must achieve a high degree of availability in readiness for fire emergency. Research has demonstrated that voice messages are more effective than conventional sounders in alerting people and directing them rapidly out of a building, because VA systems give clear instructions, tailored to the developing situation.
Although VA systems have been used in the evacuation of buildings for a number of years, the development of robust standards based on best needs for safety in case of fire has evolved more slowly. Recently, a number of new European product standards and a revision of BS 5839-8 code of practice have been published. The impact of these developments is reviewed below.
Revised BS code of practice
BS 5839-8, first published in 1998, has been used by the voice alarm industry for over 10 years. At the systematic review of this standard, the responsible BSI committee decided that it should be overhauled to adopt the same structure as BS 5839-1:2002 and introduce new thinking in the conception and implementation of VA systems. A group of industry experts assembled and revised BS 5839-8, which was eventually published in May 2008. Many of the recommendations in the 1998 edition of the code were transferred to the revised code. No major changes, except for some clarifications, were made to the recommendations for audibility and intelligibility of messages or to those for commissioning and maintenance of systems. However, a number of significant changes in other areas were made.
Need for voice alarm
Because of their effectiveness, VA systems should be used in all buildings where life safety depends on having a pre-determined evacuation plan. This covers most occupied buildings, including those where the use of traditional alarm sounders such as bells or electronic sounders may be deemed sufficient. However, in practice, the need for a VA system in a specific building will be determined by the authority responsible for enforcing applicable fire safety codes and/or by a fire risk assessment carried out by the owner, landlord, occupier or employer.
Like the 1998 edition, the revised code directs the reader to the clear recommendations of BS 5588, (of which parts 6, 7, 10 and 11 are most relevant). BS 5588 is being replaced by BS 9999, a new code of practice for fire safety in the design, management and use of buildings. It is unfortunate that, when it comes to voice alarm systems, BS 9999 only offers imprecise recommendations. BS 9999 confuses public address systems with VA systems, treating the terms as though they were interchangeable. BS 9999 does not refer to BS 5839-8, the industry accepted Code. It also fails to adequately consider the need for informative warning systems to operate reliably in the event of evacuation of a building. The danger is that BS 9999 will lead to the use of un-monitored and non-regulated informative warning systems instead of VA systems compliant with and certificated to BS 5839-8. Should this happen, BS 9999 would have failed in its intention to enhance life safety in buildings.
Types of VA systems
There are many different ways of configuring VA systems, each having different degrees of complexity and different demands at the various stages of their life cycle, from system design to daily operation. For example, systems may have different needs for manual intervention and the ensuing demand on operator training. For this reason, the 2008 edition of BS 5839-8 recommends that the type of system needed is identified at an early stage of the planning process, agreed by all interested parties and recorded in the contractual documents. Types of systems are based on the degree of operator control needed for effective implementation of the evacuation plan rather than on the size of the systems or the number of evacuation zones. The following five types are defined:
- V1 is purely automatic, responding only to alarm signals it receives from the fire detection system. Some non-emergency controls are, however, permitted
- V2 has an ‘all call' microphone facility but no alarm zone facilities
- V3 has, in addition to an ‘all-call' microphone, zone microphone facility but has no other emergency manual controls
- V4 has, in addition to ‘all-call' and zone microphones, capabilities to manually control recorded messages in alarm zones.
- V5 is intended for applications requiring a site specific engineered approach
Evacuation based on risk assessment
The safety of building occupants in the event of fire depends on having a suitable evacuation plan. The revised code introduces the concept "that the design of the voice alarm system is based on the results of a risk assessment such that potential failure to achieve satisfactory results is minimised to reasonable and acceptable levels". It recommends that a "risk-rating" assessment is conducted in order to determine the most appropriate evacuation plan, the result of which will govern the degree of manual control required and, thus, the type of system.
A pragmatic rather than prescriptive approach based on the analysis of a number of factors is set out. Hence, this risk-rating assessment should take into account the kind of occupancy, the nature of the building and the extent of the life safety risk involved. The selection of system type will then be based on assessing one or more of the following:
- the need for manual intervention
- the provision of continuing operator and staff training
- the regularity of evacuation drill
- the layout and complexity of the building
- the density of occupation
- the type of occupants, e.g. staff, members of the public, disabilities, etc
- the need for phased and/or partial evacuation
- the likelihood of any hazards, e.g. fire, bomb, nuclear and chemical spillage, civil commotion, etc
It is not possible for the code to cover and give recommendations for all possible application situations. However, in the commentary on Clause 8, examples of possible relationships between risk assessment and selection of system types are given. This should be sufficient for most people to select the appropriate system type for any given application.
The use of voice sounders
The 1998 version of BS 5839-8 warned about the limitations of voice sounders which, then, were a relatively new and unproven technology. The 2008 version recognises that voice sounders have a role to play in VA system applications. Voice sounders do not normally incorporate facilities for broadcasting live emergency messages so they are used in automatic Type V1 systems. There is no restriction placed by the code, except for governmental or local guidance documents, as to the size of installations that can be achieved with voice sounders.
Voice sounders that use loudspeaker transducer technology are capable of providing acceptable performance in the more complex acoustic environments. However, the code recognises that, due to size and cost constraints, many voice sounders use an audio sound transducer that has a more restricted frequency response than cone or horn loudspeakers. This type of voice sounder is more suitable for quiet and non-reverberant spaces than in larger and/or noisier public spaces. The code recognises that voice sounders cannot necessarily be installed with the same spacing as traditional sounders because this may be too far apart to meet intelligibility requirements. Given these limitations, the code recommends that the quantity and location of voice sounders be the same as for loudspeakers and that the same recommendations regarding intelligibility apply.
Type and protection of loudspeakers
The revised code simplifies and rationalises the recommendations for the selection of the type of loudspeaker, with the emphasis placed on the need to choose loudspeakers according to the acoustics at their location. The code does not recommend that loudspeakers should survive a fire. Indeed, it is recognised that in order to achieve intelligibility, loudspeakers, such as those utilising a paper cone, cannot be protected from fire. If a fire breaks out in a particular room the occupants can be expected to leave quickly. However, it is critical that the integrity of the loudspeaker circuit is maintained so that occupants in other areas of the building can also be alerted. To achieve this, the revised code follows BS 5839-1:2002, recommending the use of fire resistant cables and their adequate mechanical protection.
Emergency microphones and their use
In the 1998 edition of the code, emergency microphones were called "fireman's microphones", which implied that they could only be used by firefighters. In the 2008 edition these have been renamed "emergency microphones" in order to reflect their wider application in VA systems, such as their use by trained staff prior to the arrival of the fire and rescue service.
In order to broadcast intelligible messages, training and instructions in the proper use of a a microphone is essential. The code recommends that a pictogram be mounted near the microphone location illustrating both close talking and normal situations.
Networked and wireless systems
The revised code introduces recommendations for networked systems modelled on those in the 2002 edition of BS 5839-1. They mainly cover the use of fire resistant cables in all paths critical to emergency broadcast, the need to monitor network loop for continuity and the need to broadcast emergency messages within one second of the voice alarm signal being received at the sub-system.
New recommendations for systems with radio-linked components are also introduced. Although the requirements for radio-linked components are given in the new European standard, EN 54-25, the code includes important additions such as the ability of radio-linked components to provide seven days' standby plus 30 minutes' power supply autonomy, and the need to use monitored fire resistant cables for the connection to external antennae. The new clause on radio-linked components underlines the importance of a radio signal site survey, recommending that such a survey be conducted as a matter of routine.
New European standards
In 2008 two new and important harmonised European standards for VA systems were published by CEN and adopted as BS EN standards. One, EN 54-16, establishes the requirements for the control and indicating equipment (VACIE); the other, EN 54-24, establishes the requirements for voice alarm loudspeakers. One of the implications of the introduction of harmonised European product standards is the requirement to comply with the Construction Product Directive (CPD) and to CE mark products following third party certification by a notified body, such as LPCB. Although this has been voluntary for EN 54-16 and EN 54-24 since 2008 when these standards were first published, third party certification will become mandatory from March 2011 and July 2011 respectively.
EN 54-16, VACIE
Annex D of EN 54-16 describes which functions are normally included in the VACIE (see Figure 1). An important concept of EN 54-16 is that the emergency microphone(s) are an integral, albeit optional, part of the VACIE. EN 54-16 incorporates requirements for the standard or optional components of the VACIE, including visual and audible indicators, microphones, message stores, amplifiers and the interface with the fire detection and fire alarm CIE. Provision is made for combining the function of the VACIE with those of the fire detection and fire alarm CIE. In all cases, power supply equipment complying with EN 54-4 must be used.
EN 54-16 specifies the operational performance applicable to the mandatory conditions of the VACIE including the quiescent, alarm and fault warning conditions and the requirements for two optional conditions, the disablement condition and manual zone control.
To ensure adequate performance, test methods have been included that verify output power against the manufacturer's declaration, as well as testing signal-to-noise ratio and frequency response. Different frequency response is required depending whether or not a microphone is included. The VACIE must also be submitted to the same environmental and EMC tests as specified in EN 54-2 tests.
EN 54-24, voice alarm loudspeakers
The publication of EN 54-24 followed closely that of EN 54-16. It specifies the requirements, test methods and performance criteria for loudspeakers intended to broadcast a warning of fire to occupants of a building. It covers two types of application environment: type A, generally for indoor use and type B, generally for outdoor use.
EN 54-24 requires that the frequency response limits fall within a specified range (see Figure 2). It incorporates tests to verify the manufacturer's declaration as to the duration of operation at rated noise power, rated impedance, horizontal and vertical angles of coverage and maximum sound pressure level.
EN 54-24 also requires that voice alarm loudspeakers comply with the same catalogue of environmental tests as other field devices used in fire detection and fire alarm systems such as detectors, alarm sounders and visual alarm devices. It has been said that these environmental demands on loudspeakers are too excessive, will be difficult to achieve and will result in increased prices. However, it would be unreasonable to expect that components of a fire detection and fire alarm system did not comply with the standards hereto accepted in order to achieve life safety. Manufacturers of loudspeakers may need to review their design accordingly.
Conclusion
The foundations are now in place to enable the voice alarm industry to develop solutions and install systems that meet the challenges for system integrity, availability and reliability demanded by modern buildings design in case of fire. It is unfortunate, however, that this situation is still confused by the existence of the older and contradictory standard, BS EN 60849 which has remained in place in spite of the withdrawal of its international equivalent, IEC 60849. The challenge for standard makers will be to review and rationalise this unsatisfactory situation.
Bernard Laluvein is strategic product manager at Tyco Safety Products. He is vice-chairman of the Fire Industry Association's fire detection and alarm executive council, chairs FSH/12/5, the BSI subcommittee responsible for developing BS 5839-8, and is also convenor of CEN/TC72/WG3 which drafted both EN 54-16 and EN 54-24, the European standards for voice alarm control equipment and voice alarm loudspeakers respectively
