It is a common misconception that hazardous area (Haz A) compliance is applicable only to electrical components and that mechanical components always fall outside of the requirements of the Haz A certification process.
As potential sources of ignition can be created by factors other than electrical sparking, such as friction, static discharge or impact between materials, this could clearly apply to mechanical components and as such, components that have these attributes need to be considered under the Haz A assessment.
A good example of this is the Magnetic Level Gauge that is a mechanical fabrication of pipe and flanges, with the addition of a moving metallic float. The float is the vehicle to carry the magnet that operates the external display indicator which rises and falls according to the liquid level.
The very nature of an isolated moving object inside the pipe raises the potential for friction, impact forces or static electrical isolation that have the possibility to cause a potential incendive situation. Magnetic Gauges are therefore designed to eliminate these possible hazardous events by a variety of special features – examples of this are internal damping springs at the top & bottom of the pipe to absorb the float energy and provide a non-metallic barrier between the 2 metals surfaces. To overcome static charge build up, the gauge is fitted with earth bonding and/or specially engineered materials to prevent the charge building to a hazardous potential.
The outline drawing below shows a cross section through the gauge body with some of the special design features incorporated. Note – the protection concept for this design is designated Ex c (c) constructional safety, and as such an approved gauge will carry a nameplate with the full code detailing its limits of use – e.g. Ex c IIC T6
Ex - Explosion Protection
C – Protection Concept (Constructional safety)
IIC – Gas Group (Hydrogen)
T6 – Temperature class (Max 85°C)