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To be able to safely leave a structure in case of fire, escape Structure with non-metal roof and external
routes must be kept free of smoke which causes orientation lightning protection system
and breathing problems. Embedded or protruding roof-mounted structures on struc-
Smoke and heat extraction systems are both equipped with tures with external lightning protection system must be locat-
manual call points and automatic detectors which detect the ed in the protected volume of air-termination systems as per
smoke or heat produced and extract it from the escape route IEC 62305-3 (EN 62305-3) under consideration of the separa-
via electromechanically or pneumatically driven windows or tion distance s if the following limit values are exceeded:
domelights. In addition to this main function, the windows or
domelights are also used for ventilation. For this purpose, ad- Embedded or protruding metal roof-mounted structures:
ditional switching devices are available which are capable of
issuing switching commands of lower importance. Since the ¨ Height above the roof level: 0.3 m
availability of smoke and heat extraction systems must be en- ¨ Total area of the roof-mounted structure: 1.0 m²
sured even in the event of power failure, the fire control panels ¨ Length of the roof-mounted structure: 2.0 m
are equipped with accumulators which supply the smoke and
heat extraction systems. Therefore, the actuators of the win- Embedded or protruding non-metal roof-mounted structures:
dows and domelights are dimensioned for d.c. operation.
¨ Height above the air-termination system: 0.5 m
The surge protective devices in the examples described below
are dimensioned based on a voltage of 24 V d.c. which is com- Due to the above requirements, domelights of a certain size
monly used in this industry. Moreover, electromechanically must be protected against lightning strikes. If air-termination
driven domelights with a maximum nominal current of less rods are installed, the domelights are located in LPZ 0 B which
than 1.8 A or 4 A d.c. are used. means that no lightning current is injected into the equipment

motor
24 V d.c. < 4 A protective angle α
wind / rain sensor
smoke detector No. Surge protective device Part No.
DG M TN 275 (TN-S system) 952 200
DG M TT 2 P 275 (TT system) 952 110
BXT ML4 BE 24 920 324
fire control 3* + BXT BAS 920 300
panel 2*
4*
2 x BXT ML4 BE 24 920 324
+ 2 x BXT BAS 920 300
230 V / 50 Hz
BXT ML4 BE 36 (1.8 A) 920 336
+ BXT BAS or 920 300
2 x BVT ALD 36 (4 A) 918 408
6* 4* (6*)
BXT ML2 BE S 24 920 224
SDS VS + BXT BAS 920 300
=

6*
4* (6*) Alternative
TL2 10DA CC 907 991
SDS VS DRL 10 B 180 FSD 907 401
EF 10 DRL 907 498
8 x DRL RE 24 907 422
* Minimum number of required cores
(observe manufacturers’ instructions)
Figure 9.27.1 Domelight located in the protected volume of an air-termination rod on a non-metal roof of a structure with external lightning
protection system

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