The class/division system, used in North America, defines and classifies specific hazardous area conditions.
Class: the nature of the hazard, such as gas, vapor, dust and fibers. There are 3 classes in total. Class I is important for the petro/chemical industry since it covers flammable gases or vapors, with enough to cause explosive or ignitable mixtures.
Division: the probability of the hazardous material being present. There are only 2. Division 1 represents a high probability, while division 2 is low.
Group: the type of hazardous material. These range from A through G, with each group containing loosely related flammable substances. The list covers over 50 of them, from acetylene to zinc.
The Zone system is used in Europe, Asia and elsewhere internationally. Zone is gradually being adopted in North America.
Zone: the general nature of material (e.g., gas or dust) and probability of hazardous material being present in ignitable concentration.
- Zone 0 covers for long periods of time.
- Zone 1 covers what is produced under normal operating conditions.
- Zone 2 covers gases that are not likely to occur and do so for a short period of time.
- Similarly, Zone 20 covers fibers that are present continuously or long periods of time.
- Zone 21 covers normal operating conditions.
- Zone 22 covers ones that are not likely to occur and do so for short periods of time.
Group: the type of hazardous material and (partly) location. Group I covers mines. Group II covers explosive gas, while Group III covers explosive dust.
An IP number identifies the level of protection provided by an enclosure or housing. It contains two digits, preceded by “IP” (e.g., IP66). The first number ranges from 0-6 and relates to protection from solids by defining the size of solids or dust particles. The second number relates to protection from liquids and helps identify the enclosure’s liquid tolerance using varying quantities and pressures of water. It ranges from 0-8 and ranges from no protection or dripping through heavy jet sprays and immersion/submersion.
For example: IP66 = dust tight and protected against heavy water jet spray.
NEMA is a rating system that defines the environment type in which an electrical enclosure can be used and its ability to withstand various environmental conditions. The NEMA scale ranges from 1-13, with 1 covering dust, light and indirect splashing while 13 covers dust, spraying of water, oil and noncorrosive coolants and meets oil exclusion and rust resistance design tests.
In the world of mass flow products, the most common classifications are NEMA 4/4x, IP65, IP66 and IP67.