FEATURE FIRE SAFETY
FIRE CONSIDERATIONS in difficult environments
INGRESS PROTECTION A vital concern for units in hazardous environments is the ingress protection, or IP rating of the product which classifies and rates the degree of protection provided against the intrusion of dust, accidental contact, and water. Ingress protection ratings are usually
Left: Optical beam smoke detector in an explosion proof housing. Above: Flame detector in a flameproof stainless steel enclosure
Specialist fire detection products exist to serve specific applications. Solutions include aspirating detection for clean rooms/servers, or an optical beam detector for warehouses and other large internal areas. However, as the technology and the industry develop, the risks are constantly evolving
T
he most difficult environments from a safety perspective are those which are
potentially explosive. This covers a variety of industrial processes, including petrochemicals, flour mills, fine chemicals, spray booths, electronics manufacture and waste handling. Each application has a different balance of features versus cost and so knowing what is required from your equipment is a vital step in obtaining the most suitable protection. In explosive environment applications,
the risk of fire is significantly increased, in terms of both its likelihood and the severity of the consequences. The environments can also be very hostile to the fire detector, often being corrosive or dusty/dirty which may interfere with the proper functioning of the unit. Indeed, some environments are so dangerous that the fire detection device itself can pose a significant explosive risk. Virtually all modern detectors are electrical devices – shorts within the circuit can create sparks that could detonate the wider environment. As a result, units have to include special safety precautions so that no risk is posed to the protected area. These precautions can be embodied in many different ways (as per the ATEX directive), but in the marketplace, two solutions are generally used:
10 SUMMER 2016 | INDUSTRIAL COMPLIANCE Flameproof enclosures – a sealed
environment that the detector sits in. Should the unit short-circuit creating an explosion, then the unit can retain all the energy of that explosion and not ignite the external environment. Intrinsic safety – safe by circuit design,
intrinsically safe detectors limit the potential energy of an electrical device so that it cannot pose an ignition risk. This list is by no means exhaustive. Other concepts include keeping flammable gases out through pressurisation or encapsulation, as well as changing the layout of the product’s circuits to limit the energy. However, the most common solutions are flameproof and intrinsically safety. Typically, flameproof units are bulkier
and often are a little more expensive, but are substantially cheaper to install in a given application, making them the method of choice for protecting a given explosive area. On the other hand intrinsically safe devices are challenging to install, having an additional requirement for shielding any power source using electrical barriers. As a result, intrinsically safe detectors are usually only used in the most dangerous of applications, where the risk of explosion is a constant concern.
reported in the format IP ‘X’ ’X’. The first number corresponds to the dust ingress protection, while the second corresponds to how resistant the unit is to liquid ingress. A higher number represents greater resistance to that hazard (0-6 for dust, 0-8 for liquids). A unit that is marked as being IP 66 is dust tight and waterproof against powerful water jets. The higher liquid ratings are designed to test a unit that will be submerged at different depths for an extended period of time.
Ingress ratings are important as
explosive/hazardous environments may include different types of chemical/ vapours, many of which can disrupt the proper function of a detector. However, the external seal of the unit is only half the battle in dangerous environments, the material choice is also vital.
MATERIAL The material that the unit is made of is another vital attribute – what good is a unit sealed off against the atmosphere within a room if the unit itself can be attacked? As such, correct material choice is vital when installing products in dangerous environments. Housing material such as zinc alloy is cost effective, but stainless steel will often provide better protection against corrosive action. Even then, for applications such as marine environments it may be more effective to use a higher-grade stainless steel such as 316 (made with additives), rather than ‘standard’ 306 grade. This selection of materials is also important for plastics, where certain materials can go brittle or degrade under different environmental conditions. When specifying a specialist product for
a potentially explosive area, it is vital to understand the risk within the installation environment. Overlooking one aspect can detrimentally influence a vital safety feature (i.e. corrosive environment compromising a flameproof housing), so understanding the risk is critical. A provider of specialist detection equipment will be in a position to advise you on what features your detector will require to match the environment, and should be able to offer different variants depending on your risk type.
FFE
www.ffeuk.com T: 01462 444740
/ INDUST RAL COMPA RI CE
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