Page 275 - Introduction to Marine Engineering

Fire fighting and safety 249

others can operate and gradually bring the machinery back into service.
Where a machinery space fire involves electrical equipment then only
dry powder or carbon dioxide extinguishers can be used until the
equipment is isolated.

Cargo spaces
Where a fire occurs in a cargo hold with a smoke detection and carbon
dioxide flooding system fitted, the procedure is straightforward and has
already been described. It is essential to ensure before flooding that all
air entry and exit points are closed by fire dampers and all fans are
stopped.
Oil tankers with their cargo tanks full or empty present a potentially
serious fire hazard, A fire occurring in a cargo tank will doubtless lead to
an explosion or an explosion will lead to fire. The rapid use of foam
making equipment, the cooling of surrounding areas and the isolation of
the fire should immediately take place.
The prevention of fire and explosion conditions is the main
prerequisite with oil tankers. With reference to hydrocarbon vapours,
such as those present in oil tanks, the diagram shown in Figure 13.15
should be considered. The relative proportions of hydrocarbon vapour

Upper
flammable
limit
10
9 £
3
R 8 •?
Too rich

Non-flammable
T3
-C

Lower
flammable
Too weak limit

20 15 10 5
Percentage oxygen in mixture
Figure 13.15 Flammable limits