New methodology for fire suppression systems

Fire engineers at CSIRO have recently developed a new methodology for assessing the operation and performance of smoke detection and alarm systems and any linked suppression systems for early to very early detection of smoke.

Dr Atul Bhargava of CSIRO Fire Science & Technology says, "This is of particular interest in enclosures with complex temperature and airflow environments."

Typically, these are the environments encountered in freezers, large warehouses, atrium areas with high ceiling heights, and underground railway stations.

"The temperature and airflow environments in the locations where the VESDA smoke detection and alarm system was tested varied from docking and packaging areas operating at 4°C and low airflow velocities, to storage areas with both low and high airflow velocities, and temperatures ranging from -18 to -24°C."

Dr Bhargava says, "In such cases, early and very early smoke detection is of paramount importance for safeguarding assets and for providing early cues for evacuation.

"For instance, early smoke detection is of particular concern in warehouses where a fire in a highly stacked area can rapidly become very large if not detected and controlled at an early stage.

"Our methodology involves the creation of a plume of hot air by the use of radiant heaters. Artificial smoke is introduced in the centre of the plume, which moves towards the ceiling of the enclosure. The temperature and ventilation conditions within the enclosure govern the flow of smoke.

"The smoke density is monitored continuously using an optical smoke meter and the time to detection of smoke is noted," Dr Bhargava says.

"The time to detection may then be converted to the size of the fire at the activation of smoke detection for an assessment of the performance of the smoke detection system."

This methodology is based on CSIRO experience with hot smoke testing in accordance with Australian Standard AS 4391-1999 and the information contained in the Standard has been used in this protocol.

Using its new methodology, CSIRO has recently embarked on a test regime to verify the performance of the VESDA smoke detection and alarm system with its industrial partner, Vision Systems.

CSIRO was directly involved in the invention of the VESDA aspirating smoke detection system in the early 1990s and now works closely with Vision Systems to assess the performance of the systems for newer applications.

Dr Bhargava says, "We have already conducted several tests to assess VESDA's performance in freezer applications. A series of tests was conducted at commercial sites in Brisbane.

'The temperature and airflow environments in the locations where the VESDA smoke detection and alarm system was tested varied from docking and packaging areas operating at 4°C and low airflow velocities, to storage areas with both low and high airflow velocities, and temperatures ranging from -18 to -24°C.

"The most demanding test for smoke detection was in blast freezers which operated at approximately -35°C and at extremely high airflow velocities," says Dr Bhargava.

"The impact of such environmental conditions is that the smoke is not provided with sufficient buoyancy to rise up to the ceiling, and the high airflow results in a large amount of dilution of smoke and hence the sensitivity of the smoke detection system is critical to the early detection of potential fire."

Dr Bhargava says that the testing demonstrated the success of the testing methodology developed by CSIRO, and also showed that the VESDA smoke detection and alarm system was able to detect smoke in most of the tests.

"The only scenario where the VESDA system did not detect smoke was when the smoke source was located directly beneath the air extraction vent. This was the worst-case scenario, which resulted in the direct uptake of smoke by the extraction system without allowing for the smoke to reach the sampling point of the VESDA system."

It is expected that this methodology and further work conducted by CSIRO will soon be recognised and accepted by other testing and approval authorities around the globe.