Hazardous Area Computers from Computer Dynamics

To allow for operator interface in hazardous environments, specially designed hazardous area computers or monitors must be utilized. Hazardous environments usually contain amounts of explosive gases or dust either during normal operation or during an abnormal circumstance. The function of hazardous area computers and monitors is to provide computer controls or information while preventing or containing an explosion. This can be accomplished by protecting the operator interface system from its environment, or protecting the environment from the operator interface system.

Hazardous area computers and monitors must comply with some of the most stringent safety guidelines defined by worldwide regulatory agencies. To increase the potential for global marketability, the United States has incorporated the IEC (International Electrotechnical Commission) Zone system into a parallel classification system to the traditional U.S. Class I Division system -- the U.S. Class I Zone system. The key concepts of the IEC system include area classification, gas grouping, temperature codes, protection methods and markings. Under both the Division and Zone systems, hazardous area computers for use in explosive gas atmospheres are identified based on designations that address:

• The likelihood that the explosive gas atmosphere is present when hazardous area computers or monitors are operating (see the Division and Zone designations in Table 1);
  
  
• The ignition-related properties of the explosive gas atmosphere (see the Gas Group designations in Table 2);
  
  
• The maximum surface temperature of the equipment under normal operating conditions (see the Temperature Code designations in Table 3); and
  
  
• The protection method(s) used by the equipment to prevent ignition of the surrounding atmosphere (see the Protection Method designations in Table 4).