Fast, reliable smoke detection for the dustiest settings

Aspirating smoke detection is designed for reliability and can be customised to minimise false alarms and maintenance, while increasing safety.

DEL WILLIAMS

Early smoke detection is often critical for suppressing fires quickly. In some settings, such as manufacturing facilities, voluminous dust and particulates from various products and processes can be confused with smoke by most traditional, or passive, smoke detection systems, triggering ongoing alarms. Resolving these alarms often requires excessive troubleshooting and maintenance to keep the system functional. When this is the case, prevalent nuisance alarms may compromise safety.

Although most manufacturing facilities deal with some level of dust, there is no more challenging environment that illustrates the need for advanced detection systems to distinguish dust from smoke than inside a dust collection system. Fortunately, even within this dustiest of environments, aspirating smoke detection (ASD) technology can be an effective option.

According to Khaleel Rehman, director of development for Honeywell’s advanced detection fire team, advanced ASD systems can significantly reduce both false alarms and the need for maintenance, while increasing safety, by detecting smoke at the earliest possible stage through numerous sampling points.

The process draws in air through durable piping and analyses it using sophisticated laser-based imaging and photodiode technology. Continuous sampling of air drawn from the protected area through the pipe network to the sensing unit provides the fastest possible smoke detection rates. This effectively allows the system to distinguish between actual smoke and dust or particulates, and all but eliminate nuisance alarms. The core technology has been used for decades in sensitive applications such as cleanrooms and data centres where early smoke detection is critical.

While these systems are quite flexible, many facilities use different processes and materials in varying volumes with unique facility layouts.

Extreme dust: a smoke detection and maintenance challenge

In a manufacturing process at an aluminium tubing provider, a fine hot zinc powder is spray coated onto tubing in a spray booth area. The excess powder is then directed to a dust collection system consisting of large-diameter ducting and paperbased filter media before clean air is vented outdoors.

The zinc dust accumulates quickly and abundantly inside the ducting and can easily overwhelm the filters, requiring excessive inspection and frequent maintenance to keep the system fully operational, according to Mike Angstadt of Flagship Fire.

His colleague Joseph Albert noted, “When technicians would do routine maintenance every few months on sections of ducting, they would bang the sections with a rubber mallet to remove several inches of zinc dust that accumulated inside of this duct work.”

The dust-laden, paper-based filter media would also periodically catch fire when ignited by a stray spark.

“Even though the deflagration index of the dust is low enough that providing explosion protection is not required, the plant sought greater safety with early smoke detection and fire suppression inside the dust collection system,” Mr Angstadt said.

An ASD system was used to draw air samples continuously through holes in durable industrial pipe mounted along the walls and ceiling, analysing the air in a flair detection chamber using a short wavelength laser, a CMOS imager and multiple photodiodes that could distinguish between smoke and dust, minimising false alarms. The system is cross-zoned with thermal detectors inside the dust collection filter area.

This approach allowed plant operators to manually discharge the high-pressure, carbon dioxide (CO2) fire suppression agent as needed, or for it to activate automatically if a fire occurred after hours.

Some minor adjustments were also required to increase system reliability, such as angling the air sampling points away from the most voluminous air flow sources.

According to Mr Angstadt, the smoke detection system has performed well since the installation, in conjunction with the thermal device and automatic CO2 fire suppression system, to minimise false alarms and improve early smoke detection.

Above Dust and particulates can be confused for smoke by detection systems, triggering false alarms.