Apollo manufactures intrinsically safe (IS) detectors in both the Series 60 and XP95 ranges. This is because there are many places where an explosive mixture of air and gas or vapour is or may be present continuously, intermittently or as a result of an accident. These are defined as hazardous areas by BS 5345:1976, the code of practice for installation and maintenance of electrical apparatus in potentially explosive atmospheres. Hazardous areas are common in petroleum and chemical engineering plants and in factories processing and storing gases, solvents, paints and other volatile substances. Electrical equipment for use in these areas needs to be designed so that it cannot ignite an explosive mixture, not only in normal operation but also in fault conditions. The two most common ways to achieve this are flameproof enclosures and intrinsic safety. Flameproof equipment is contained in a box so strong that an internal explosion will neither damage the box nor be transmitted outside the box. The surface must remain cool enough not to ignite the explosive mixture.

When flameproof equipment is interconnected, flameproof wiring must be used. This method is most valuable when high power levels are unavoidable but it is not acceptable for areas in which an explosive gas/air mixture may be continuously present or present for long periods.

For this reason, Apollo fire detectors are made intrinsically safe rather than flameproof. Intrinsically safe equipment operates at such low power and with such small amounts of stored energy that it is incapable of causing ignition:

• in normal conditions
• with a single fault
• with a combination of any two faults

In any of these conditions, every component must remain cool enough not to ignite the gases for which it is approved.

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