Paper is combustible, and, while solid blocks of paper may not ignite easily, once they have caught fire flames can spread rapidly and in most cases are extremely difficult to extinguish. The likes of paper and board, loose paper and shrink-wrap material can all ignite and start a fire.
Every year, fires occur in the paper and board industry, some are small and others are devastating: people are injured (on occasion fatally) and there is damage to buildings, equipment and materials. Thus, it is necessary to ensure that operations have the necessary detection, suppression and protection in place to handle fire risks.
Evaluating the risks
In paper mills the various sources of ignition cannot be completely eliminated. Some of these sources include static discharges, hot surfaces (steam pipes or infrared dryers), electrical sources (overloaded conductors), sparks (hand tools), frictional heating (hot bearings), naked flames (welding equipment or gas-fired plant). For optimum fire protection these ignition sources need to be controlled.
In most instances fire and the risk of fire arise from the likes of poorly maintained equipment, faulty or misused electrical devices, welding, poor storage of packaging materials and poor storage or handling of flammable liquids and gases. Once a fire breaks out it will spread rapidly if there is an accumulation of waste material, poor housekeeping, unsegregated storage of materials, excessive stocks of paper in the production areas, un-banded and end-stacked reels of paper, a lack of fire separation between floors or rooms and/or inadequate and inappropriate fire detection and extinguishing equipment.
The first item for any operation is to cultivate a culture of good housekeeping. The United Kingdom HSE’s Guidance on fire risks compiled by the Paper and Board Industry Advisory Committee recommends the following:
* Trim and/or waste should automatically be removed wherever possible.
* A cleaning programme needs to be implemented. Cleaning should be frequent enough to prevent any build-up of broke, dust or other waste and paper making machines need to be cleaned regularly. Office and storage areas also need to be included in the cleaning.
* Clearing away broke etc. from the paper machine should be standard procedure as part of planned shutdowns.
* Particular attention should be paid to those areas where broke paper, dust or trim is produced, as this is easily ignited. Dust will accumulate on ledges and beams and this should be regularly removed with vacuum equipment.
* Pay attention to housekeeping in other areas such as engineers’ stores, where packaging material needs to be promptly and safely removed.
Each individual mill needs to conduct a risk analysis to determine the best fire protection, detection and suppression equipment to use. Alien Systems & Technologies is able to conduct this analysis and also offers a range of products suitable for the risks identified. Generally, possible fire hazards include storage facilities and materials, paper dust, fires in machine hoods, starch, hydrogen sulphide, charging of electrically operated lift trucks, flammable liquids and electricity.
The entire operation needs to be fitted with conventional fire protection systems such as sounders, bells, manual call points as well as smoke and heat detectors. Detectors are extremely important as early warning systems allow for the quick detection of fire and immediate suppression which leads to minimal damage, downtime and possible injuries.
Hot bearings on conveyor belts are also a potential source of ignition. A product such as the PyroScan3 is specifically designed for the protection of areas where a movement of materials with a fire potential is a routine occurrence or the transport mechanism is susceptible to fire. It employs enhanced infrared monitoring technology that enables the detection of both small glowing embers within direct sight of the sensor and black body low energy sources buried within the transported material that would not be registered by other types of flame, spark or ember detector. By the use of both optical filtering and electronic analysis of the various parameters the system is blind to visible light from the sun or local luminaires, whilst being able to detect relatively low temperature material moving through the field of view.
The advantages of cloud chamber technology
A new development in fire detection is the Cirrus Pro range which works particularly well in paper mill applications as it is not sensitive to dust. Certain problems arise when utilising laser based aspirating fire detection systems as they analyse air samples for smoke particles. Smoke and dust particles are similar in size so a filter system needs to be used to differentiate between the two. If this is not maintained false alarms are triggered. The Cirrus Pro is an aspirating fire detector that uses cloud chamber technology to detect a fire in its true incipient stage before smoke even begins to be emitted.
The incipient stage of a fire is when an object begins to overheat but there is not smoke yet, just invisible combustion particles. These particles are drawn into the pipe network which channels them into a cloud chamber. Here, the tiny invisible particles are exposed to humidity, which causes them to form visible water droplets and collectively creates a cloud. Optical components detect the cloud and trigger an alarm. The particles are far smaller than dust so the system is able to differentiate between them and ensure a more accurate detection process.
Gas flooding fire extinguishing systems can be used to protect computer suites, data stores and the like from fire. A product such as the Pyroshield fire extinguishing system is environmentally friendly and poses no risk to people. The system can be actuated by detection and control equipment for automatic system operation and also equipped with remote manual actuation as required. A system such as Pyroshield is particularly useful for extinguishing fires in hazards where an electrically non-conductive medium is essential or desirable; where clean-up of other agents presents a problem; or where the hazard is normally occupied and requires a non-toxic agent.
In a paper mill application there are a variety of other precautions that can be utilised, but as mentioned before, it is best for an individual risk analysis to be done. Despite a decline in injuries by fires in paper mills in recent years, there are still a number of fires which have occurred throughout the world and caused considerable financial loss. The potential for multiple fatalities remains. Potential fire risks need to be managed and assessed. In any industry the aim needs to be to stop a fire starting and if one occurs, prevent it from spreading and ensure personnel can escape safely. As per the United Kingdom’s HSE’s guide it is important to ensure the quantity of flammables is kept to a minimum, flammable material is handled safely, sources of ignition are excluded and good housekeeping standards are maintained.
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