Beyond Hazardous Area Classification Mechanical Equipment Ignition Sources

Introduction

In deflagration incidents, electrical arcs and electrostatic sparks are often considered to be primary ignition sources, because they are “everywhere” and can have sufficient energy to ignite most flammable gases and vapors and dense clouds of many combustible dusts. However, there is a wide variety of other ignition sources ^1,2,3. In Table 1, you can see a list of different ignition types in an approximate descending order of ignition risk [ignition energy x likelihood of encountering in a chemical plant].

Mechanical equipment in manufacturing sites can present significant non-electrical ignition hazards. Hazardous Area Classification, to manage the selection and installation methods of electrical devices, traditionally only addresses the ignition hazards of electrical equipment. Mechanical equipment such as bucket elevators, mixers and blenders, and rotary air-locks can cause frictional heat or frictional sparks during routine operation or during equipment-upset conditions. To identify – and eliminate or control – these types of ignition sources, an analysis method known as a “Mechanical Equipment Ignition Risk Assessment” [MEIRA] can be used.

Mechanical Equipment Ignition Risk Assessment

It is important to limit the scope of a MEIRA to equipment or locations where a flammable gas or vapor – or a combustible dust cloud of sufficient concentration – could occur, since the above equipment could also be present at many non-hazardous locations in a chemical plant. However, if electrical or electrostatic ignition sources are identified during the MEIRA, they should also be reported, perhaps separately.