Hazardous atmospheres may be classified as :
• Non explosive athmosphere : the athmosphere doesn’t contain explosive elements and all kinds of standard products can be used .
• Explosive Atmosphere : The atmosphere contains potentially explosive elements , both gas and dust. Explosive atmospheres are defined as ” hazardous area ” countries IEC as ” HAZLOC ” in North America .
The equipment for explosive atmospheres is designed , installed , operated and maintained according to international standards and local regulations regarding these dangerous areas or areas casos.Les ( Hazardous Areas ) defined by 4 items :
• Temperature Class
The following relevant parameters characterize the potentially explosive atmosphere :
• Frequency with which the explosive atmosphere can exist
• Ability gas or dust to an explosion .
The explosive gas and dust is classified according to its ease suffering ignition , according to its characteristics:
• Minimum Ignition Energy
• Minimum temperature of ignition
• Self- ignition temperature
• Temperature layer ignition
EN1127 -1 : 1997
Explosive atmospheres – Explosion prevention and protection – Part 1 : Basic concepts and methodology
IEC 60079-10 : 2002-06
Electrical equipment for explosive atmospheres – Part 10 : Classification of hazardous areas
IEC 61241-10 : 2004-06
Electrical equipment for use in presence of combustible dust – Part 10 : Classification of areas where there is or may have combustible dust .
National Electrical Code ( National Electrical Code ) . Issued by AISI (American National Standards Institute ) and NFPA 70 (National Fire Protection Association)
The standards define the areas described :
|> 1000 h||The explosive atmosphere is present continuously , for long periods or frequently|
|10 h … 100 h … 1000 h||The explosive atmosphere can occur during normal operation as usual .. |
|< 10 h||The explosive atmosphere should not be given during normal operation . But if it happens , will last only for a short period of time .|
In the United States , the ” old ” standard referenced by NEC 500 is still in force. The new NEC Article 505 and 506 includes a classification of areas and installation requirements similar to IEC standards defined above
|Atmosphere||Ârea HAZLOC NEC 500||Definition|
|Gas or dust||Division 1||concentrations that can ignite gas , steam air mixtures , combustible dust and fibers may be suspended in normal operating conditions .|
|Gas o dust||Division 2||concentrations of gases that can be started , steam air mixtures , combustible dust and fibers may be suspended in extraordinary operating conditions .|