FOCUS
Suppression options Activated by heat sensors inside the
trommel or flame detectors at the trommel exit, the water swamps the trommel from the inside. This does not cause damage to the trommel itself or to the rotating screen, it just means a rather wet clean up exercise afterwards. The real challenge is to keep the deluge nozzles clear of debris, and to avoid damage by the rotating contents. Also, drilling the casing of the trommel might void warranties from the trommel supplier if it is not first agreed with them as an acceptable thing to do.
On conveyors Conveyors do ‘what they say on the tin’: they convey materials from one place to another, and in a complex waste handling facility there can be a good number of such conveyors crisscrossing the lofty shed at multiple levels and in multiple layers in a bedazzling array. They all have a job to do and they do it well, with a high degree of reliability and effectiveness. The main challenge with conveyors (apart
from stopping ‘fall-off’ – see below) is that if a fire occurs, they can also be the means by which the fire spreads rapidly across the building. Brand new conveyors are coated with oil, and if a fire occurs during installation or commissioning of a new plant, it is the surface oil that will rapidly spread a fire, not any combustible waste material. Conveyor belt material is largely rubber,
which will burn quite well if subject to sufficient heat. The cost of fire retardant conveyor belt material is several times the cost of standard conveyor belt material, which results in most waste operators using the standard belts and managing the risk through maintenance, cleaning, emergency response and, in some cases, fire protection. Most waste handling sites will have open
conveyors, and if a roof level sprinkler system is installed, it will afford a degree of protection. The problem is that roof level sprinklers are static and respond to a build up of heat generated in the static space beneath them. Conveyors on the other hand are in motion, and any fires they carry will move far too quickly to activate roof level sprinklers. Only when the conveyor has been stopped
will roof level sprinklers be able to respond, but as mentioned previously, they are primarily designed to protect the building structure, not to save the conveyor or other equipment below. Installing fire protection on conveyors is done to tackle fires in the material that is being conveyed, and to prevent the conveyor
36 NOVEMBER 2018
www.frmjournal.com
belt material from becoming involved. The aim is to detect and extinguish a fire locally and to save the conveyor structure, the belt and the waste if possible. In practice, for typical waste handling
facilities, dedicated conveyor fire suppression is not installed on open conveyors, as the fire risk is considered sufficiently low that manual emergency response, fire and rescue service action and any roof sprinklers if installed will be sufficient. However, the use of localised deluge waterspray protection over critical conveyors or transfer points could be considered, although the use of fire detection and appropriately arranged machine interlocks would suffice in most cases. This changes though if the material being conveyed is particularly combustible, if there are no roof sprinklers installed, or if the building is particularly lofty. Most often, fixed
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