Hazardous ATEX Locations
The Directive ATEX is named after the French " ATmospheres EXplosives" and has been mandatory from 1st July 2003. The ATEX Directive consists of two EU directives describing what equipment and work environment is allowed in an environment with an explosive atmosphere such as fixed offshore platforms, petrochemical plants, mines, flour mills and other areas where a potentially explosive atmosphere may be present. Areas classified into zones are divided into zones 0,1 and 2 for gas/ mist and 20, 21 and 22 for dust. Equipment and protective systems intended to be used in zoned areas must meet the requirements of the directive.
ATEX Zones
Zone 0 - An atmosphere where a mixture of air and flammable substances in the form of gas, vapor or mist is present frequently, continuously or for long periods.
Zone 1 - An atmosphere where a mixture of air and flammable substances in the form of gas, vapor or mist is likely to occur in normal operation occasionally.
Zone 2 - An atmosphere where a mixture of air and flammable substances in the form of gas, vapor or mist is not likely to occur in normal operation but, if it does occur, will persist for only a short period.
ATEX Directive
99/92/EC ATEX 137 (formerly 118a), often referred to as ‘The user’s directive’, is concerned with safe working conditions and is implemented in UK law by the Health & Safety Executive in the form of the Dangerous Substances and Explosive Atmospheres Regulations, or DSEAR. ATEX 137 requires the end-user to define what the equipment manufacturer can lawfully supply.
94/9/EC ATEX 95 (formerly 100a), often referred to as ’The Manufacturer’s Directive’, is concerned with ATEX product compliance. This enables the equipment manufacturer to supply product that meets or exceeds the minimum requirements of the end-user’s DSEAR risk assessment.
ATEX Temperature
Temperature Class T1 to T6 defines the auto-ignition temperature of a gas, therefore the maximum temperature on the shell of an electric motor. Temperature classes vary from T6/85°C to T1/450°C but the most popular are T4/135°C and T3/200°C. As examples only, ATEX codes could take the form Ex II 2G IIB T4 for Zone 1 and Ex II 3G II T3 for Zone 2. Take care with Hydrogen gas; it has T1 the lowest auto-ignition risk but Gas Group IIC the highest incendive properties.
Hazardous Classes Locations
Hazardous Location Types
Class 1 Locations
According to the NEC, there are three types of hazardous locations. The first type of hazard is one which is created by the presence of flammable gases or vapors in the air, such as natural gas or gasoline vapor. When these materials are found in the atmosphere, a potential for explosion exists, which could be ignited if an electrical or other source of ignition is present. The Code writers have referred to this first type of hazard as Class I. So, a Class I Hazardous Location is one in which flammable gases or vapors may be present in the air in sufficient quantities to be explosive or ignitable. Some typical Class I locations are:
- Petroleum refineries, and gasoline storage and dispensing areas
- Dry cleaning plants where vapors from cleaning fluids can be present
- Spray finishing areas
- Aircraft hangars and fuel servicing areas
- Utility gas plants, and operations involving storage and handling of liquified gas or natural gas
Class 2 Locations
The second type of hazard listed by the National Electrical Code are those areas made hazardous by the presence of combustible dust. These are referred to in the Code as "Class II Locations." Finely pulverized material, suspended in the atmosphere, can cause as powerful an explosion as one occurring at a petroleum refinery. Some typical Class II locations are:
- Grain elevators
- Flour and feed mills
- Plants that manufacture, use or store magnesium or aluminum powders
- Producers of plastics, medicines and fireworks
- Producers of starch or candies
- Spice-grinding plants, sugar plants and cocoa plants
- Coal preparation plants and other carbon handling or processing areas
Class 3 Locations
Class III hazardous locations, according to the NEC, are areas where there are easily-ignitable fibers or flyings present, due to the types of materials being handled, stored, or processed. The fibers and flyings are not likely to be suspended in the air, but can collect around machinery or on lighting fixtures and where heat, a spark or hot metal can ignite them. Some typical Class III locations are:
- Textile mills, cotton gins
- Cotton seed mills, flax processing plants
- Plants that shape, pulverize or cut wood and create sawdust or flying
Hazardous Location Conditions
In addition to the types of hazardous locations, the National Electrical Code also concerns itself with the kinds of conditions under which these hazards are present. The Code specifies that hazardous material may exist in several different kinds of conditions which, for simplicity, can be described as, first, normal conditions, and, second, abnormal conditions.
Division 1 - In the normal condition, the hazard would be expected to be present in everyday production operations or during frequent repair and maintenance activity.
Division 2 - When the hazardous material is expected to be confined within closed containers or closed systems and will be present only through accidental rupture, breakage or unusual faulty operation, the situation could be called "abnormal."
Nature of Hazardous Substances
The gases and vapors of Class I locations are broken into four groups by the Code: A, B, C, and D. These materials are grouped according to the ignition temperature of the substance, its explosion pressure, and other flammable characteristics.
Group A - The only substance in Group A is acetylene. Acetylene makes up only a very small percentage of hazardous locations. Consequently, little equipment is available for this type of location. Acetylene is a gas with extremely high explosion pressures.
Group B - Group B is another relatively small segment of classified areas. This group includes hydrogen and other materials with similar characteristics.
Group C - Group C Consists of flammable substances such as Ether.
Group D - Group D is made up mostly of hydrocarbons, various fuels and solvents.
