August 20, 2017

Risk analysis and prevention of conveyor belt fires

Fire, especially on conveyor systems can result in catastrophic consequences that can negatively impact on a mine’s operation. Typically lives and equipment damage are at stake when it comes to such events. Therefore conveyor fire belt detection systems plays a pivotal role in the elimination or reduction of fire break-out that might be costly to any organization.

There are multiple conveyor fire belt detection systems in the market, however there is no one size fits all solution. Hence, before choosing a suitable solution/s from multiple systems available, it is imperative that a total risk analysis is carried out to determine potential high risk areas along the conveyor belt, e.g. pulley bearings, explains Jan Mulder, Market & Support Manager at Sperosens.

Risk assessments provides the information required to determine the applicable system amongst the various tools found in the market. In addition to risk analysis, it is important that fire prevention becomes part of the whole strategy- thus preventing fire from breaking-out from high risk areas identified is vital rather than providing a reactive cure when fire breaks-out. The strategy should include measuring belt temperature, temperature around the conveyor as well as carrying out preventative maintenance in order to prevent fires from breaking-out which might result in lost productive time and lives, Jan Mulder elaborates.

Temperature scanners, bearing temperature sensors, flame detectors, smoke sensors, etc. are also used as part of the broader strategy. It is therefore critical that double- redundancy is applied to address concerns about undetected faults. For instance if one system fails the second will kick in, thus eliminating room for error. Multiple detection methods such as early detection and flame detection tools should be used in order to eliminate any errors that may result because of fault detection tool. However, Allowance should also be made to allow for manual over rider, should the automatic system fail.

Some of the detection tools available on the market today, include the following: early detection and flame detection tools, as well as the bearing temperature sensors, that monitor the temperature of the bearing.

Early Detection tools include the Plumber block temperature sensor (analog or digital) 68℃ – maintenance alarm and belt stop,the IR Temperature scanner- 68 ˚C – Maintenance alarm and belt stop, as well as the 90˚C – Fire alarm and spray system activation. In addition, both Plumber block temperature sensors and IR Temperature scanner, allow for temperatures to be monitored on surface.

Flame Detection includes the Triple spectrum IR Flame detector, flame- Fire alarm and spray system activation, and the Linear Heat Detection wire- 68˚C, 88˚C, 105˚ C- Fire alarm and system activation.

After detecting the fire, it is important to use the correct method of suppression as per the risk assessment, in adherence to National Fire Protection Association (NFPA 15 or 16 etc.) set standards. These would include foam systems, water sprinkler systems, clean gas agents etc.

The system design addresses critical components such as the belt coverage, flow rate, nozzle selection, pipe diameter as well as the duration and capacity requirements of for fire protection system chosen. For instance in terms of duration and capacity requirements, the NPFA 15 requires the system to spray for 30 minutes as well as an additional 30 minutes for backup. It should have the capability to activate two zones simultaneously, or at least one zone plus a fire hydrant. The flow rate of a fire hydrant is typically 1200l/min, Jan Mulder adds.

Measuring the health of the system in use is critical; the system should be working 24/7 in case something happens, therefore the controllers in use should be able to send the signal immediately to the control room if system malfunction is detected, and the system should be regularly cleaned and maintained, Jan Mulder concludes.

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