LASER BASED SMOKE DETECTORPresentation by

GOWTHAM R

SVCE

REQUIREMENT REGARDING SMOKE DETECTORS

According to FSS code (INTERNATIONAL CODE FOR FIRE SAFETY SYSTEMS), Chapter 9

Smoke detectors are to be operated before the smoke density exceeds 12.5% obscuration per metre, but not until the smoke density exceeds 2% obscuration per metre.

WHAT IS LASER?

LASER is an acronym of ‘Light Amplification by Stimulated Emission of Radiation’

PECULIAR PROPERTY OF LASER

A laser differs from other sources of light from a point that it emits light coherently

LASER BASED DETECTORS

LASER BASED DETECTOR

HOW IT WORKS?

Laser based detectors works on the light-scattering principle, but with greater sensitivity.

This ultra-sensitivity is due to the nature of the laser itself, which is literally an amplified light.

Using an laser diode, the laser beam is transmitted through the chamber to a light trap which eliminates any reflection.

The integral lens focuses the light beam to a very small volume near the receiving photo sensor(not on photo sensor but on light trap)

The photo sensor is activated by a scattering of smoke particles in this small-volume light beam.

A special mirror reflects and concentrates most of the scattered light into the photo sensor.

DESIGN OF THE MIRROR

PERFORMANCE

Currently there are two smoke sensing technologies in use

ionization and

Photoelectric (either scattering or obscuring type)

Both technologies have different strengths.

Ionization detectors detect fast-flaming fires well — but are not so quick with slow-smoldering fires.

Photoelectric detectors detect slow-smoldering fires well — but are not so quick with fast-flaming fires.

Laser type detectors are highly sensitive to both types of fire.

ADVANTAGES OF LASER BASED DETECTORS

Dust rejection

Very Intelligent Early Warning (VIEW) smoke detection

Higher accuracy

Low standby current than ionization type

How dust rejection is possible?

DUST REJECTION

In normal photo-electric smoke detectors, dust can settle in the detection chamber.

Over time this dust increases the amount of reflected light in the chamber making the detector more prone to false alarms.

Since LASER BASED DETECTOR focuses beam of laser light, reflections are minimized in the chamber.

EXTENDED APPLICATIONS

The range for detection can be varied for a wide range from .06%/meter to 6.41%/meter. Thus this detector setting can be varied according to various applications.

Lased based detectors can also be fitted in continuous aspiration smoke detection systems for detecting fire in cargo holds.

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