VoidAlert™ & BS5839-1:2017

‍Fire Alarm systems require ongoing maintenance and detection devices should be tested at least once per year so provision should be made for all detectors to be accessible.  Again, in ceiling voids this can be a significant challenge.

VoidAlert™ answers so many of these areas of concern but does it comply with BS5839?

Read our FAQs to find out.

FAQs

What type of Automatic Fire detector is VoidAlert™ as defined by BS5839-1:2017?

VoidAlert™ is a digital Line Type Heat Detector as referred to in BS5839-1:2017 at Para 21.1.2: “Heat detectors may take the form of either point type detectors or line type detectors. The detection system may be designed to respond when a fixed temperature is reached.”  It offers continuous heat detection down its entire length.

Why is it called “Digital” Line Type Heat detection?

According to Cambridge Online Dictionary, “digital” means “recording or storing information as a series of the numbers 1 and 0, to show that a signal is present or absent”  It is used in this context in contrast to “analogue” which is defined by the same dictionary as “using a system in which information, such as sound or images, is stored or sent in a continuously changing form, such as electrical signals, radio waves, or film”.  The type of line type cable used in VoidAlert™ has two states – either normal, i.e., under its critical operating threshold or fused, i.e., above its threshold temperature.  The transition from normal to fused state is irreversible.

Do you mean ‘once it operates it can’t be reset’?  I expected that it would behave like a normal heat detector.

Digital Line type heat detection cable is not resettable once it has transitioned from normal to fused state.  However, provided the cable has been correctly installed (i.e., not run in the immediate vicinity of uninsulated steam pipes or other excessive heat sources), the only time the cable should ever operate is if there is a fire.  If the cable fuses as a result of detecting a fire, there are going to be more significant matters to worry about and the cable can be repaired in any case.

None of this is to be confused with “silence alarms” and “reset” functions of the Control and Indicating Equipment which will behave and operate as they would for any other type of fire detector or call point device.

Can the cable be jointed?

Yes, the cable can be jointed provided that the recommendations of BS5839-1:2017 Para 26.2 g are followed.

This all sounds too good to be true.  Are there any situations where VoidAlert™ is not recommended?

VoidAlert™ provides heat detection not smoke detection.  In systems specifically designed for the earliest warning of fire, smoke detection is recommended.

BS5839-1:2017 defines Category L1 systems as automatic fire detection and fire alarm systems intended for the protection of life where the systems are “installed throughout all areas of the building.”  It states that “The objective of a Category L1 system is to offer the earliest possible warning of fire, so as to achieve the longest available time for escape;” (clause 5.1.3 a) refers)

Similarly, at para 5.1.4 it defines category P1 systems as “automatic fire detection and fire alarm systems intended for the protection of property” where systems are “installed throughout all areas of the building.”  It states that “The objective of a Category P1 system is to offer the earliest possible warning of fire so as to minimize the time” (clause 5.1.4 a) refers)

For this reason, we recommend that VoidAlert™should only be installed in category L1 or P1 systems after the potential consequences of delayed notification of a fire have been considered by relevant technical authorities.  BS5839-1:2017 provides a mechanism for this to be done via a “variation” (Section 7 of the standard refers).

In a particular application it might be considered that the advantage of the Line Type Heat Detection outweighs any possible delay of notification, in another application the risk might be unacceptable.  In both cases, we recommend that the Variation process is used to allow the client to make an informed decision.  

What about a situation where Fire Alarm is required to be Category L3 and we have a room with a void separated from an escape route via a fire-resistant structure?  There is also a void over the escape route.

In this instance:

• Optical smoke detectors should be used on the ceiling of the escape route.
• Fire detectors (e.g. Voidalert™) may be used in the void above the escape route.
• Any type of fire detector, other than a flame detector, should be used in the room opening onto the escape route.

Nothing is needed in the void above the room opening onto the escape route because with L3 category specified we are protecting the escape route.  If there was a fire in the void above the room opening onto the escape route, then it would have to pass through the room or the void over the escape route, to get to the escape route. Due warning will therefore be given.  

This would also apply to similar locations in L2 systems. Point type fire detection should be installed in voids over high-risk rooms in L2 applications.

How should VoidAlert™ cable be positioned?

BS5839-1:2017 para 22.6 provides recommendations for siting of line type heat detectors and the guidance it contains should be followed when positioning VoidAlert™ cable as follows:

a. Line heat detectors should be sited in such a way that no point in the protected space is further than 5.3 m horizontally from the nearest point on a line heat detector.

b. If the protected area has a pitched ceiling, for line heat detectors at or near the ceiling, the figure of 5.3 m given in 22.6a) should be increased by 1% for each degree of slope up to a maximum increase of 25%. For line heat detectors not at or near the apex the distance given in 22.6a) applies.

c. The recommendations of 22.3d), 22.3e), 22.3g), 22.3j), 22.3k) and 22.3m) apply.

d. Where a line heat detector runs closer than 500 mm to any wall, partition, or obstruction to the flow of hot gases, such as structural beams and ductwork, then that section of the line heat detector should be discounted from providing detection.

NOTE Those parts of a line heat detector within 500 mm of the control equipment need not be considered for the purpose of this recommendation.

e. Where a line heat detector is installed to protect a particular item of plant or cabling, as opposed to providing general area protection, the detector should be mounted as close as possible to the place where fire or overheating might occur, and either be mounted above the risk or in thermal contact with it.

22.3d) In apex roofs, fire detectors should be sited at or near each apex, except that, if the difference in height between the bottom of the roof and top of the apex is less than the following figures, the roof may be treated as flat (see Figure 7):

1) 600 mm if the area is protected by smoke detectors;

2) 150 mm if the area is protected by heat detectors.

NOTE 4 Detectors may be regarded as “near the apex” referred to in 22.3c) and 22.3d) if the vertical distance from the apex to the detector is within the figures given in 22.3d)1) and 22.3d)2) for the appropriate type of detector.

22.3e) Other than within rooms in a Category L3 system [see 22.3f)] or in voids [see 22.3g)] or where a horizontal ceiling comprises a series of small cells [see 22.3l)], fire detectors should be sited on ceilings, such that their sensitive elements are between the following distances below ceilings: 25 mm – 150 mm for heat detectors.

22.3g) In unventilated voids not greater than 1.5 m in depth, the sensing element of fire detectors should be sited within the top 10% of the void or the top 125 mm, whichever is the greater

22.3j) Where an area contains partitions or storage racks that reach within 300 mm of the ceiling, the partitions or storage racks should be treated as walls that extend to the ceiling (see Figure 10).

NOTE 10 Where a rack contains high-value or high-risk materials or where the height of the rack exceeds 8 m, the use of in-rack detection might be considered. For more information, see the FIA Code of Practice for Design, Installation, Commissioning and Maintenance of Aspirating Smoke Detector (ASD) Systems [7].

22.3k) Ceiling obstructions, such as structural beams, deeper than 10% of the overall ceiling height should be treated as walls [see Figure 11a)].

NOTE 11 Within horizontal voids, beams or obstructions that are deeper than 10% of the overall depth of the void, regardless of whether the void is above the ceiling or below the floor, ought to be treated as walls that subdivide the void.

NOTE 12 For a cellular structure or closely spaced beams in a void, see 22.3l).

22.3m) Detectors above a perforated false ceiling may be used for protection of the area below the false ceiling if:

1) the perforations are substantially uniform, appear across the complete ceiling and throughout they make up more than 40% of the surface; and

2) the minimum dimension of each perforation in any direction is 10 mm; and  

3) the thickness of the ceiling is not greater than three times the minimum dimension of each perforation.

How should VoidAlert™ systems be zoned?

As VoidAlert™ offers continuous heat detection down the entire length of the installed cable, if it detects a fire, it is not possible to identify the exact point at which the fire occurred.  For this reason, the area covered by a single detector should be carefully considered and the stipulations in BS5839-1:2017 regarding Zone size should be followed.

Your attention is drawn to section 13 of the standard, in particular those comments which apply to Zones which contain non-addressable automatic fire detectors:

13.2.1 Recommendations applicable to all detection zones

The following recommendations are applicable.

a. [Relates to Manual call points]

b. If the total floor area of the building is greater than 300 m2, each zone should be restricted to a single storey.

c. If the total floor area of the building is less than 300 m2 a zone may cover more than a single storey.

d. For voids above or below the floor area of a room, these may be included within the same zone of the room, provided that the voids and the room constitute a single fire compartment.

13.2.3 Additional recommendations applicable to detection zones that contain non-addressable automatic fire detectors

The following recommendations are applicable.

a. The floor area of a single zone should not exceed 2 000 m2.

b. The search distance (see 3.52) should not exceed 60 m.

NOTE 1 Having entered the zone, the person responding to the alarm signal need not reach the seat of the fire within the recommended search distance; it is only necessary to become aware of the location of the fire.

NOTE 2 In measuring search distance, the worst case, in which the fire is located at the furthest concealed area from any likely point of entry to the zone, ought to be considered (see Figure 2).

c. Automatic fire detectors within any enclosed stairwell, lift well or other enclosed flue-like structure should be considered as a separate detection zone. Manual call points located at final exits to open air from stairwells may be incorporated within these detection zones [but may, alternatively, be incorporated within the detection zone described in 13.2.1a)].

Got a question about VoidAlert™? Need help with the installation of VoidAlert™? Get in touch today!

For over 45 years, Fixfire® has been providing quality products, systems and services for Life & Property Protection. Whatever your requirement please call our Compliance Team for expert advice and a refreshingly different approach.

Freephone 08000891999

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