Managing fire risk is critical to waste recycling
30 November 2010
Much of the waste being combustible is particularly susceptible to fire due to the nature of the processing machinery which includes shredders, hammer mills and rotary shearing machines.
Managing fire risk is critical to waste recycling
All these machines exhibit high frictional forces which induce heat into the material ultimately leading to fire. The risk will differ between plants subject to the volatility of the materials being recycled. All plants processing waste combustible material will have an incident eventually.
Fortunately management today are becoming more aware of the risk of fire and its implications regarding the safety of the operators, extended down-time and the high costs to repair or replace burnt out plant.
The installation of water sprinkler systems is perhaps the most common approach to the fire hazard within a waste processing plant and one that is frequently endorsed by the insurance industry. Whilst sprinklers are effective and limit the spread of a fire they are triggered by the fire itself which may already have caused considerable damage to the plant and building.
The essence of sensible fire management is to be able to identify the point at which the fire starts and thereby nullify its potential to spread very early on in the combustion cycle. It will be clear to the reader that the fire is the product of a fuel which is ignited in the presence of oxygen. Consequently by removing the ignition source or any one of the other parameters combustion will not take place.
Ignition may be in the form of a spark, flame or more commonly a glowing particle such as a nail or a smouldering ember. The ability to detect and extinguish each source of ignition is paramount to the successful policing of a waste processing facility.
What are the requirements of a fire prevention system?
Detectors – insensitive to daylight
Detectors should be insensitive to daylight thereby preventing false alarms. Utilising passive infra-red optics they need to be robust and capable of installation within the process and be able to detect sparks, flames and glowing particles down to 150°C. To limit the number of detectors required each detector should have a 360° wide angle view of the target area they are policing and be able to trigger extinguishing mechanisms in less than 100mSecs
Efficient extinguishing makes the difference between success and failure
An efficient high speed extinguishing system is of equal importance to the detector in any fire prevention system. Water extinguishing with a specific droplet size is key to the suffocation and cooling of the ignition source. Whilst reaction speed is also critical to full development of the extinguishing zone, typically 400mSecs, so too is the placement of the nozzles within the process area. In addition the nozzle design should be maintenance free with a high pressure capability of up to 9bar.
There are a number of fire prevention systems on the market which use different technology. As mentioned earlier sprinklers are by far the most common protection system but rely on flames to break a glass before extinguishing can be effective. In many cases the damage done by the water deluge can be excessive rendering the plant idle for some days. CCTV is also used with key positions being monitored from a control area relying on manual operation of the extinguishing points. This is likely to cause a delay in release of the extinguishing water allowing the fire to take hold.
Another approach and one that is gaining more acceptance is the use infra-red detection based systems. Detectors are installed at strategic points within the process to provide very early warning of glowing particles or flame produced from shredders, mills or other process machinery. On indication extinguishing water is released onto the glowing particle for a few seconds nullifying its potential to cause fire further downstream. This is repeated for each glowing particle without interruption to the process. Where the frequency of glowing particles exceeds a pre-set threshold, or flames are indicated, then the water nozzles remain open and the plant is shut down. Water nozzles throughout the plant can be triggered in sequence to prevent the spread of fire from machines down or upstream of the detection point.
With the very real potential of fire within the waste recycling business some manufacturers are addressing the problem head on to meet the needs of both plant and range of materials being processed. One such company, Firefly AB of Sweden, offers a tailored solution to the waste recycling industry in the form of their ‘ShredderGuard’ system distributed in the UK by Orthos Engineering.
Firefly, are a risk management company with over 30 years experience in protecting industrial processes developed the ShredderGuard to meet the demands of an expanding industry which is particularly at risk from the onset of fire. The system encompasses a bespoke design package to deal with all the potential risks across the plant and is one of a series of systems available to protect a number of industrial processes.
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