Buildings and Structures 2

Fire Detection Systems

Aim

To provide students with information to allow them to recognise the common types of fire detection systems found in buildings and structures.

Learning OutcomesAt the end of the session students will be able to state:

• The functions of a fire detection system

• The main components of a fire detection system

• The principal operating systems

• The most common types of detector.

Function of detection systems

To detect one or more changes in the protected environment that indicate the development of a fire condition.

Fire detection systems Will operate when;

• The invisible products of combustion are being released

• Smoke is being produced

• The temperature in the vicinity of a fire rises rapidly or reaches a preset figure.

Types of detectors

• Ionisation

• Optical

• Radiation

• Heat

Smoke detectors

Choice of detector system is based on the risk and the circumstances surrounding that risk; Reliability, cost and robustness.

Types of detectors

• To protect life

• To protect property

• A combination of the above, either simultaneously or at different times or places.

Detection systems are installed for the following reasons;

British standard for detectors

BS 5839 PT1 gives the definition of a detector, the principal factors are;

• At least one sensor that constantly or at intervals monitors at least one suitable physical and / or chemical phenomenon associated with fire

• It provides a corresponding signal to the control and indicating equipment.

Operating signal for detectors

The signal to operate an alarm to warn of fire or to operate automatic fire protection systems can be made at the detector or at another part of the system such as the control and indicating equipment.

Ionisation type.

Ionisation type.

Optical type.

Optical type actuated by smoke.

Radiation type.

LENS & FILTER

INFRA RED RADIATION

PHOTO ELECTRIC CELL

INTEGRATOR TIMER

FILTER AMPLIFIER

ALARM

Heat detectors

• Designed to detect fire in its more advanced stages

• Three basic operating principles

Melting or fusion of plastics / metals

Expansion of solids, gases or liquids

An electrical effect (tilt switch).

Types of heat detector

• Fixed

Responds when a set temperature is reached

• Rate of rise

Responds to abnormally rapid increases in temperature.

Heat detectors.

Sprinkler systems.

Confirmation Assessments will be based on this lesson and the corresponding study note

Learning Outcomes• The functions of a fire detection system • The main components of a fire detection

system• The principal operating systems• The most common types of detectors.

THE END