Instrumentation/control systems ignition sources

Detonation arresters are typically used in conjunction with other measures to decrease the risk of flame propagation. For example, in vapor control systems, the vapor is often enriched, diluted, or inerted, with appropriate instrumentation and control (see Effluent Disposal Systems, 1993). In cases where ignition sources are present or pre-dic table (such as most vapor destruct systems), the detonation arrester is used as a last-resort method anticipating possible failure of vapor composition control. Where vent collec tion systems have several vapor/oxidant sources, stream compositions can be highly variable and... 

The sparking of electrical equipment, such as motors, is a major potential source of ignition, and flame proof equipment is normally specified. Electrically operated instruments, controllers and computer systems are also potential sources of ignition of flammable mixtures. 

At the surface, the ignition wells for use with downhole electric heaters must have a high-pressure lubricator, stuffing box, flttings, also necessary measurement and control instruments (Fig. 62). The equipment includes a special electric cable of correct length, AC current source, and an air supply system. Special care must be taken to protect the stuffing box seal from electric current. 

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