Page 266 - Introduction to Marine Engineering

Fire fighting and safety 241

Accommodation , Machinery
space

Sprayers
Section
0
\ S?*' " , To fire main valve
alarm valve fresh
water
Test Test * J"""*-*-** Test valve To fire
valve valve
mam
Connectini valve -W-i X Section
; (locked shut) ± J vatve
n \ Sprinkler Sprayer; ; ' ^ ^ ^
t
Test pump
valve Test valve s *"'** n
Accommodation Machinery (b) Sprayer system
{a} Sprinkler system space
Figure 13.10 Automatic water spray systems, (a) sprinkler system; (b) sprayer system

The complete installation is divided into several sections, each containing
about 150 to 200 sprinklers and having an alarm valve. When one or
more sprinklers operate water flows through the section valve and
sounds an alarm and also provides a visual display identifying the section
containing the fire.
In the machinery space the sprinkler heads are known as 'sprayers'
and have no quartzoid bulb. Also the section valves are manually
operated to supply water to the sprayers (Figure 13.10(b)). The system is
pressurised by compressed air with a salt water pump arranged to cut in
automatically if the pressure drops. The accommodation and machinery
space systems may be combined by a valve which is normally kept locked
shut.
The system should be regularly checked by creating fault conditions at
the various section control valves by opening a test valve, and checking
for audible and visual alarms.

Water mist (Jog)
Water mist (fog) sprinklers are being used as an alternative to, the now
banned, Halon fire suppression systems. The mist system delivers very
small water particles, which are able to remain suspended in the air. The
water particles are evaporated by the heat of the fire and the expanding
vapour displaces oxygen. The combined cooling and oxygen starvation
effects quickly extinguishes a fire. Less water is used than with sprinkler