Page 325 - International safety guide for oil tankers and terminals

SAFETY AND FIRE PROTECTION

smoke particles, photo-electric light obscuration or light scattering,
electrical resistance changes in an air chamber and optical scanning of a
---ใช้เพื่อการศึกษาเท่านั้น---
cloud chamber.

Gas (Product of Combustion) Sensing Fire Detectors are designed to
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
sense and respond to one or more of the gases produced during the
combustion of burning substances. These detectors are seldom a
preferred option as fire tests have shown that detectable levels of gases
are reached after detectable smoke levels.

Flame Sensing Fire Detectors are optical detection devices that respond
to optical radiant energy emitted by fire. Flame detectors responsive to
infra-red or ultraviolet radiation are available, but ultraviolet sensitive
detectors are generally preferred.

19.2.5 Selection of Fire Detectors

When planning a fire detection system, detectors should be selected
based on the types of fires that they are protecting against. The type and
quantity of fuel, possible ignition sources, ranges of ambient conditions,
and the value of the protected property should all be considered.

In general, heat detectors have the lowest cost and lowest false alarm
rate, but are the slowest to respond. Since the heat generated by small
ึ
fires tends to dissipate fairly rapidly, heat detectors are best used to
protect confined spaces, or located directly over hazards where flaming
fire could be expected. To avoid false alarms, the actuation temperature
of a heat detector should be at least 13°C above the maximum expected
ambient temperature in the area protected.

Smoke detectors respond faster to fires than heat detectors. Smoke
detectors are best suited to protect confined spaces and should be
installed either according to prevailing air current conditions or on a grid
layout.
Photoelectric smoke detectors are best used in places where smouldering
fires, or fires involving low temperature pyrolysis, may be expected.
Ionisation smoke detectors are useful where flaming fires would be
expected.

Flame detectors offer extremely fast response, but will warn of any
source of radiation in their sensitivity range. False alarm rates can be
high if this kind of detector is improperly used. Their sensitivity is a
function of flame size and distance from the detector. They can be used
to protect areas where explosive or flammable vapours are encountered
because they are usually available in explosion-proof housings.

19.2.6 Location and Spacing of Fire Detectors

Fire detection at marine terminals is usually provided at remote,
unmanned, high risk facilities, such as pumping stations, control rooms,
and electrical switch gear rooms. Detectors may also be fitted at valve
manifolds, loading arms, operator sheds and other equipment or areas
susceptible to hydrocarbon leaks and spills, or that contain ignition
sources.

To function effectively, fire detection devices must be properly positioned.
Detailed requirements for spacing can be found in appropriate fire codes.

© ICS/OCIMF/IAPH 2006 291