Line of Sight Oil mist and Smoke Detector

Iceweb aims to raise the level of awareness of a relatively new technique being used to detect the presence of oil mists and smoke particles. This product has huge potential in our opinion for the early detection of oil mist releases or smoke. In Australia this has particular relevance because of the Westralia incident this year (1998). The Westralia was an Royal Australian Navy Auxiliary tanker. Unfortunately this vessel had a serious engine room fire caused by a diesel release and several people died. This type of incident is not confined to Australia however and is a common reason for ship fires.

The I.R 6003 line of sight oil mist and smoke detector was developed by Shell Thornton, and is now marketed by Wormald Fire Systems.

Principle of Operation

As indicated, the I.R. 6003 is a line of sight device. The transceiver generates a modulated infra red beam from an 820 nm GaAs source. This light beam is projected from the transceiver to a specially designed cone reflector and back again. If anywhere along the path of detection, the beam becomes incident to mist or smoke, the IR light is refracted (scattered) and the received signal is greatly diminished.

The light scattering is a function of the particle size and shape, refractive index of the particle and the wavelength of the incident radiation. Complex calculations and predictions have been made and used to determine how the received signal will appear after passing through a cloud of smoke or mist.

Specific algorithms programmed into the device allow it to distinguish between beam blockages and alarm conditions. More recently, advanced signal processing have been introduced into the unit, allowing the detector to be used in external / exposed environments. By adding neural networks into the device, further analysis on the scattering characteristics differentiates between oil mist / smoke and other non-hazardous particles such as water mist and fog.

If the beam becomes blocked and remains so for an extended period of time, an alarm is raised. This alarm is distinguishable from a true alarm condition.

Applications

The I.R. 6003 comes as

either

a smoke or a mist detector. As well as this, it is also available in rapid or moderate response times. The rapid response time should be used in critical applications where immediate action must be taken. The moderate response unit takes a few seconds longer to report as the signal is integrated to give better accuracy and less spurious alarms.

The use of intelligent electronics enables monitoring of large areas of a plant, whilst still being highly sensitive and suitable for use even in "still air" conditions.

The 4 possible combinations make it a suitable device for many different applications.

The matrix below specifies what model to use for varying operating conditions.

	Detection Mode
Response Time	Mist	Smoke
5 - 6 Seconds	Model 1 I.R. 6003 / 1	Model 3 I.R. 6003 / 3
10 - 12 Seconds	Model 2 I.R. 6003 / 2	Model 4 I.R. 6003 / 4

Developing this further:

Model I.R. 6003 / 1

Used for situations where immediate action upon detection is required. Typically this would be areas like turbine enclosures, pump rooms, engine rooms and lube oil pipework.

Model I.R. 6003 / 2

This would be used where immediate action is not necessarily required. The signal is integrated to minimise spurious alarms. This would be used in open areas and other pipe work.

Model I.R. 6003 / 3

Once again for emergency situations, used in large areas to avoid the need for many point type detectors. Typical areas include warehouses and aircraft hangers

Model I.R. 6003 / 4

Essentially the same areas as above or any other area where fire is a threat, but with the extra caution against spurious alarms.

Installation

The installation of the I.R. 6003 is similar to any other line of sight device, with the exception of a few special considerations. Wormald offer a range of products to aid in the installation and alignment of the transceiver.

As with any LOS device, before the unit is fitted, it is important to contemplate the following.

Any prevailing winds / air currents.
Pockets of high smoke / oil concentration.
Obstacles to the flow of the particles.
The most optimum detector placement pattern.

Areas that are likely to need detection.

Areas that are common are engine rooms, turbine enclosures, and oil lines, especially around flanged joints and welds.

There are special considerations that should be adhered to if the unit is to be used as a smoke detector. In order to conform to BS 5839 (BS 5839 covers fire detection for buildings ). The detectors need to be mounted at least 2.7 metres from floor level and no more than 500 mm from the wall. The beam of the detector should not be within 500 mm of a wall or partition.

Technical Data

Operating Voltage	10 - 40 Volts
Q Current	26 mA
Maximum Alarm Current	70 mA
Beam Length	2 - 50 m
Weight	0.96 kg
Material	Polymer (Noryll GTX Grade 80) IP65
Operating Temperature	-10 - 55 ° C
Certification	Baseefa EEX ib IIB T5 Loss Prevention Council BS 5839 Part 5
Miss Alignment	Max 50° off Orthogonal - Up to 40° in the one plane.
Features	m P self checks at power up. Local and remote alarming and healthy alignment signals. Functions correctly on up to 90% of signal reduction due to fouled lenses. Indication of dirty optics. 2 wire operation allowing direct replacement of point types. Watchdog timer to detect electronics fault. No circuit adjustments - configuration and alarm sensitivity set by software. The first instrument to meet the standards of the loss prevention council. m P allows serial communication to obtain more analogue information or further signal processing.

Advantages over conventional techniques

The main advantage that this device has over its rivals is the large plant coverage that is achieved from just the one unit. This means better coverage, less maintenance, less cables, less configuration and testing and ultimately less cost.

Traditional oil mist detection is normally performed using pellistor gas detectors which try to detect the small amounts of gas that are dissolved in the oil. This has proven unreliable due to the insufficient amount of gas released from the oil and because the oil poisons the gas detector material.

Conclusions

The I.R. 6003 appears to be the beginning to a new wave of oil mist detection and an efficient means of detecting the presence of smoke.

The unit seems to have all the functionality and finesse of a first grade detector of oil mists and smoke. This combined with the favourable laboratory and field test results measured highlights its use in both onshore and offshore situations.

The I.R. 6003 has clear-cut advantages and would be ideally suited for use in personnel and equipment safety designs - especially in ship engine rooms.

Thanks to Tim Byrne for this article.