Getting a handle on intrinsic safety

Speaker photo

Ravindra Jagasia, R.Stahl Inc.

At our mid-September meeting, Ravindra Jagasia, North American Sales Director – Automation for R. Stahl Inc., spoke on intrinsic safety. Electric devices that are certified as intrinsically safe under certain hazardous atmospheres will be unable to ignite an explosion.

PhotoJagasia began his presentation with a representation of a triangle that described the ingredients necessary to create a plant explosion. At the apex is an an electrical or thermal ignition source of sufficient energy. At the two bottom angles are fuel and oxygen. Fuel includes flammable gases, vapors, and combustible dusts or fibers.

He explained that the certification for the United States and Canada differs from that for Europe. The U.S. and Canada organize hazardous areas by classes, divisions, zones, and groups. The ATEX certification of the European Union refers to a system based on zones. Both are currently working towards a uniform standard.

In North America, he says, Class 1 areas contain flammable gases, vapors, or liquids. Within this class, Division 1 areas have flammable materials that exist under normal operating conditions. In Division 2 areas the hazards are not likely to exist under normal operation. Division 2 further divides into two zones defining the length of time hazardous materials can exist in the area under normal conditions. In a third zone the flammable materials exist only under abnormal conditions.

Jagasia said that article 504 of the National Electric Code provides a definition of intrinsically safe. This article covers ways to remove the source of ignition by a Zener barrier or a galvanic isolation. The Zener barrier limits the voltage and current that can enter a hazardous area. This limits the power and energy entering. Examples of galvanic isolation include transformers and fiber optic circuits.

Jagasia continued his presentation with ways to improve safety with the use of explosion proof cabinets, purged cabinets, seals, redundant Zener diodes, low capacitance cables, grounding practices, and properly spaced wiring installations.

A copy of his presentation slides will be posted soon.


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