Fire prevention

Published:  05 August, 2010

Fire prevention is a big issue in production engineering and manufacturing, particularly where the application of heat is an integral part of the process. However, not only are the requirements of each plant different but within each plant there are multiple applications that demand unique measures for detection, suppression and control. Here Chad Relf, of fire safety system specialists Industrial Design Ltd, outlines some typical applications from the food and beverage, automotive and tobacco sectors and explains how to achieve effective detection and fire extinguishant in each case. 

Irrespective of the industry sector, there are some things that are common to every manufacturing or process plant in the world. One of these is that there is always a fire risk for which we need to plan. As a result, when I'm first contacted by a potential customer, the initial process I go through is the same.

The first step is to gather as much information as possible about the application. This involves discourse with the client, background research into the risk and, normally, a site visit. During such a visit we look at the process or equipment that needs protection and ask a member of the client"s team to demonstrate it and explain its operation and to identify any specific areas of risk.

Once the type and location of the detection is determined we decide where to put storage cylinders, pipe work and nozzles to get the optimum performance from the system whilst taking into account any restrictions caused by the equipment or processes. As part of this process the customer’s production programme and shift patterns need to be discussed to try and minimise any disruptive effect that the installation of the equipment may cause.

Compliance issues must also be considered.  All systems should comply with current appropriate legislation (e.g. EN15004, BS5306 and BS5839) unless otherwise agreed with the appropriate authority.  This may further depend on the Customer’s in house regulations, site location and insurance company requirements.

Health and safety is a primary concern with all systems, both during the installation phase and during the ongoing use of the completed system.  Risk assessments and method statements need to written, agreed and complied with during the installation phase and the system user must likewise adhere to agreed procedures during its ongoing use.

This is the point where the differences between each project and each sector begin to really become clear. For instance, in the food and beverage industry, we often come across packaging machinery where they use heat based shrink wrapping and carton sealing processes, which have been known to cause fires. Product can get jammed on the conveyor and, because heat is applied in the chamber, the jammed item will burst into flames.  In addition mechanical faults, such as bearings running hot, can generate sufficient heat to cause a fire in a device such as a polythene film packaging machine.

In these applications we would normally use ultra violet or infra-red detection to provide a very rapid alert; required because of the quick burning process. The extinguishing system would probably be carbon dioxide applied using the local application method to extinguish the fire and cool the residue.

Another issue in food plants is deep fat frying; which is of course a common process applied to everything from potato chips and vegetables to meats and fish. The problems here are caused when the oil is raised above its flash point or when ultra heated product that has been immersed in oil for an extended period is exposed to the air. The latter often happens during cleaning, when the oil is emptied out of the vat and the product residue left in the bottom spontaneously combusts.  

Here we recommend the use of heat detectors, to detect the rise in temperature, and carbon dioxide for extinguishing. This suffocates the fire by preventing oxygen from supporting re-ignition as well as cooling the combustion source to below its spontaneous combustion level. As an alternative to carbon dioxide, we also consider water mist. The water turns to steam during discharge and combines with the by-products of combustion to create a fire suffocating blanket. This also provides a cooling effect, thus reducing the oil’s temperature.

Another industry to consider is the tobacco sector. The process of preparing the tobacco, and also the process of making it into cigarettes and then packing and wrapping them in primary and secondary packing can create potential hazards. Polythene or cellophane packaging can result in problems similar to those found in the food industry.

Furthermore, fires caused by faulty electrical or mechanical equipment are possible in tobacco and packaging storage areas. Because the storage facilities can comprise large open areas with high, densely packed racks, high sensitivity aspirated smoke detection is often recommended for the early detection of a fire.

Unique challenges

The automotive industry also creates a unique set of challenges. One example is the hazardous paint stores often found in a car plant. In many cases these areas are classed as hazardous because of the presence of stored solvents and other flammable liquids. These can require explosion proof fire detection and alarm equipment. 

Our preference when undergoing the design process is to position the gas cylinders outside the hazardous area. If, in exceptional circumstances, this cannot be achieved, they can be located inside the hazardous area using explosion proof components.

Another paint related hazard can be found in large electro-static spray painting booths, where the electro static reaction can cause the paint to ignite as its is sprayed out of the guns; effectively turning them into mini flame throwers!  Here the remedy is use ultra violet flame detection, which activates a discharge of carbon dioxide vapour through the paint spray lines thus effectively blowing the fire out of the spray gun and extinguishing it in the same action.

The lubrication medium often presents hazards as well.  This can be the oil used in gear hobbing or the paraffin used in bore honing machines or the oil in quench tanks, which can also be prone to spontaneous combustion. These types of fires can be detected using thermostatic heat detection to activate uniquely configured carbon dioxide systems.

One hazard area that is common to all three industry sectors I’ve covered so far is the computer room. The risk here is normally of electrical fire, which requires point type smoke detection and an extinguishing system using an inert gas such as nitrogen or argon. However, these gases need large storage areas so if space is at a premium we opt for FM200 or Novec 1230; manufactured gases that require smaller extinguishing concentration and thus take up less storage space.

The essence of the problem is that where you have extreme heat there is the risk of fire. Nevertheless, by attending to the individual demands of each sector and, as in the examples we have discussed, the individual needs of the machines found in each industry, unique designs can be produced which share a common result; effective detection, suppression and control.

For further information please visit: www.industrialdesign.ltd.uk

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