TECHNOLOGY RESEARCH AND DEVELOPMENT More Than Alarm Anna Kołodziej-Saramak The purpose of the voice alarm systems (VAS) is to inform people about hazards in a possibly efficient way (which, unfortunately, cannot be achieved using only alarm signals). They make it possible not only to give the alarm but also to convey important information, for instance evacuation guidelines. Complying with current requirements, operational, high-tech voice alarm system cannot always guarantee effective evacuation. The following constant external factors influence significantly illegibility of a verbal notification: properties of the building (architectural structure), its complexity, purpose (use regime), cubic capacity of the rooms, acoustics of the interior, room arrangement (so-called open space), wall and ceiling decoration (materials absorbing or reflecting an acoustic wave). The verbal notification may be influenced also by volatile external factors, like people and changing nature of the threat. Message Without Interference The message transmitted through VAS should be comprehensible. Audibility is very often identified with intelligibility, which is incorrect. Appropriate sound level is necessary but cannot guarantee intelligibility. Loudness does not necessarily entails high level of intelligibility which can be observed e.g. in rooms with long reverberation time. In such acoustic conditions, the message we receive, despite the high volume, is distorted, since what we receive is mostly the reflected wave. Hence, bad acoustic conditions cannot be compensated with loudness. Unfortunately, this often takes place in different buildings. Distorted by the reverberation, the message may be unintelligible despite sufficient or even high volume level. Therefore, the intelligibility of the message is reduced because of the low share of the level of sound reaching directly our ear and the high share of diffused sound as well as because of too low value of the sound level of the signal emitted through the VAS in relation to the background level (the noise around). The level of noise in the surroundings should be of fundamental meaning and should be taken into consideration in equipping buildings in VAS. Nowadays it is possible to obtain such data without making surveys in the whole building as there are average data concerning the specific nature of particular types of buildings; e.g. it is 1
assumed that 65 db is an average level of office noise. These data are proved in practice only if there are no deviations from the average acoustic conditions. It is more complicated if the building has a non-standard structure, decoration, use regime or location (e.g. it is a building located near a very noisy industrial infrastructure). In such cases a precise analysis and detailed survey are necessary. Making a survey concerning the intelligibility of a message may take place only when the room is fully arranged (decorated and furnished). The materials used for interior decoration and the way the furniture is arranged have a great influence on the speech intelligibility. Therefore, it is required to make an intelligibility survey always after any arrangement changes or renovation works influencing significantly the room décor. Quieter - Louder Specifying the volume level of a message, it is necessary to take into account the noise made by firefighting equipment which switches on automatically when the alarm starts. The equipment is an additional source of noise increasing the environment noise level. We have experienced it many times that a (mechanical) smoke extraction system decreased the message intelligibility level from good to unacceptable. One of the solutions involves a higher number of loudspeakers to decrease the distance between a hearer and the source of sound and the VAS regulating automatically the volume level of a message depending on the current level of environment noise (however, such solutions have to be always adapted to acoustic conditions in a given building, as the increase of the message level may cause its unintelligibility). Meeting the requirements concerning the background noise level in an alarm center is even more important as the firefighter s microphone is located there. Because of the specific conditions in which this device is used (for conducting the evacuation action, when the messages are transmitted directly by the action commander), it is of highest priority in transmitting the message. Therefore, there should be appropriate acoustic conditions in the VAS center (the background noise level cannot exceed 40 db). A message from a firefighter s microphone is much more imperfect. This is caused by both the influence of the individual features on the voice production and pronunciation and by the influence of the surroundings of the alarm room (a high number of operating devices increases the background noise level). Where and How In alarm centers there are usually server rooms, image registers, safety devices, battery backups. There are also control panels of different safety systems (e.g. VAS, fire alarm system, CCTV). The location of a VAS center should always be chosen with consideration of the 2
current or planned structure and arrangement of the building. Such a room has to meet many requirements: appropriate marking, proper location (near the exit), limited and supervised access to VAS appliances (only for authorized trained staff), preserving appropriate acoustic conditions. It is also necessary to maintain appropriate environmental conditions. The room should have ventilation and air conditioning because of the following: considerable amount of thermal energy emitted by the running appliances, locating the batteries in VAS boxes which can generate chemical compounds harmful for users, the necessity to provide conditions meeting the requirements of the appliances installed inside: boosters, feeders, controllers and their accumulators. To achieve those conditions the following parameters have to be fulfilled: ambient temperature from 5 to +40 centigrade short-term boundary values, relative humidity from 25 to 90 percent, air pressure from 86 to 106 kpa. Taking into account work comfort of the persons staying inside, temperature of 20 centigrade and humidity of about 45 percent constitute the optimal conditions. The room used for alarm center should be additionally controlled with smoke detectors and equipped in a manual call point. No elements which could cause electromagnetic interference (e.g. telecommunication transmitters) can be located near an alarm center. This is of special importance as during electromagnetic compatibility research the exposure levels for lines inside the alarm center are lower than for lines running outside (e.g. loudspeaker signal lines). Requirements concerning the VAS appliances specify the way the appliances are configured: they should be installed in special connection boxes and the arrangement of the room equipment should enable both the supervisors and the system maintenance technicians to use the appliances without any problems (e.g. it is necessary to provide a 75 centimeter access space to the control panel and the buttons should be at the height of 140-150 centimeters). Site plans and keys to all the rooms in the building should also be in an alarm center. It is also a good idea to locate there a computer with software enabling visualization of a signal from a fire panel, which indicates the incident site on a plan of the building. It is also important to have appropriate electrical system which complies with the needs of the alarm systems installed inside. The central switch-room should supply energy directly to the VAS control panel; however, switching off the master power switch cannot interrupt power supply to the VAS. It would be good for the master power switch to have a special safety device for the VAS control panel. It is advisable to use measures preventing unjustified or involuntary switching off the energy source (e.g. warning signs or access limiting measures). It is necessary to provide the control panel with emergency power supply, e.g. by accumulators which can provide energy to 3
keep the system working for at least 24 hours and later to keep it in standby mode for at least 30 minutes. Evacuation Tools If a firefighter s microphone is installed in other room than the VAS control room, those appliances have to be connected with a fireproof optical fibre using transceiver signal converter or with a copper cable with appropriate resistance. There are three possible configurations of a firefighter s microphone in VAS. The first and the easiest one involves using the microphone which is in the VAS control room. Usually it is a hand-held microphone equipped in a switch speak and connected to the control panel with a flexible cable. The second solution which is used involves a dynamic omnidirectional microphone installed on an inflexible or flexible arm. Definitely, the microphone should have a windscreen protecting it from air blasts when plosives are pronounced. Of course, those microphones are appropriately protected to prevent access by unauthorized persons. Usually they are located inside the control room behind glass front door equipped in a lock with a key. Sometimes the control-desk of an operator in an alarm room plays the role of a firefighter s microphone. In this case, the emergency mode is on when the key is turned. This solution can be classified as belonging to the first group as the microphone does not have any additional jacket and is an integral part of the VAS control panel. Another solution used in VAS involves firefighter s microphones which are not integral parts of the control panel. They have their own jacket, sometimes also additional power supply if an optical fibre is used. The location of an alarm center for those microphones is determined by the results of qualifying research which will be presented in the further part of the article. The last and most popular solution involves a firefighter s microphone installed outside the control room. It enables the firefighter to conduct evacuation in one of the spots where the microphone is installed. It also gives a better view on the situation than e.g. in the case of conducting the evacuation from a remote alarm center which does not have CCTV. To a great extent the number of external microphones depends on the capacities of the VAS control room and size of the building where the system is installed. The choice of the location is determined mainly by the level of resistance to the environmental influence. The possibility to install a microphone in any location would be in the interest of all the VAS manufacturers, but it is possible only if specific requirements are met. Those tests are conducted during qualifying research in the Department Laboratory of Fire Signaling and Fire Automation of the Scientific and Research Center for Fire Protection. In a 4
test of a firefighter s microphone located directly near the VAS control panel in an alarm center (A type) the exposure levels are lower than for a microphone designed to be used outside the alarm center (B type). An example: when testing the resistance to cold of an A-type microphone, temperature in the climatic chamber is -10 centigrade while for B-type microphone the temperature is much lower (-25 centigrade).the above mentioned exposure levels are used for B-type microphones because it is much more difficult to forecast and specify the environmental conditions outside the alarm center. A firefighter s microphone is a very important device in the case of an evacuation which has not been specified in a fire safety plan. Therefore, it is a very important issue to train the staff responsible for evacuation action. Persons authorized to use a firefighter s microphone should be regularly trained to make using the microphone a standard activity for them in the case of an action. In a stressful situation causing increased emotional strain such training is essential as it influences minimizing the risk of conveying the message in a nervous way and without logical arrangement. The way the message about a threat is conveyed is essential for an effective evacuation. Therefore, one should aim at achieving the best quality of messages which entails their best possible illegibility. No serious incident requiring using a firefighter s microphone in extreme conditions in the case of a direct real threat to the life of building users, has been recorded since the obligation of using voice alarm systems was introduced in Poland. Let s hope that the competences of the persons using a firefighter s microphone as a tool for conducting an evacuation action will not be verified in a situation of a real threat, as the consequences of lacking competences may be tragic in this case. Anna Kołodziej-Saramak is a deputy director of the Department Laboratory of Fire Signaling and Fire Automation in the Scientific and Research Center for Fire Protection in Józefów Types of a firefighter s microphone: a) A type installed in a VAS control panel, b) A type installed outside a VAS control panel, c) B type installed outside an alarm center 5