Viewpoint: picking the right switch for hazardous locations

Explosions can occur to varying degrees of size: all that is required is a fuel, oxygen and an ignition source.

Therefore when choosing a switch, several considerations will come into play. Firstly a design engineer needs to consider the geography and specifically the country – where the system will be deployed.

Standards, rules and regulations that have to be met in Brazil may be very different from those in Europe and vice versa. Understanding those requirements, and ensuring that your choice of switch matches the relevant approvals, is essential.

Size is perhaps the second consideration. Design engineers often have a limited space envelope in which the switch needs to be incorporated and this can have a significant impact on the range of switches from which they can choose.

Perhaps the most important consideration is the environment in which the switch is going to be used. Many hazardous locations can be outdoors so the functionality over a wide operating temperature is crucial

Further consideration of the application can come from determining which electrical ratings apply and which style of actuator is required to capture the mechanical movement to convert the action into an electrical signal.

However, perhaps the most important consideration is the environment in which the switch is going to be used. Many hazardous locations can be outdoors so the functionality over a wide operating temperature is crucial.

Switches can be found in all manner of applications, such as in blowout prevention systems used to seal, control and monitor erratic pressures and uncontrolled flow that occur during oil and gas drilling.

Using oil production as an example, switches are vital for the safety of the crew, rig and environment and to maintain the oil or gas well. If a disruption occurs an emergency system can disconnect the rig from the well, automatically triggering a switch that closes the blowout preventer (BOP) and choke valves.

Switches can also be found in mud pumps, devices used in drilling to pump mud around the cutting area to keep that area wet and lubricated and prevent a build-up of pressure.

Whatever switch you choose, and whatever the environment, pick a manufacturer that you can trust with your life

Volumes are controlled by measuring the frequency of the pumping actions which can be ‘counted’ by a switch that detects the electrical signal generated by each operation.

A further use is to detect the stability of a drilling rig, to detect lateral drift and cut the power to the drill if too much lateral movement presents a danger. Switches are also used to indicate the position of pipeline ‘pigs’, used to clear the pipe of any debris to eliminate potentially damaging blockages.

Unfortunately, not every hazardous environment where switches are required is immediately obvious.

The challenge for the designer is that different environments have diverse hazardous designations and often require different agency approvals.

In choosing a switch for a particular application, the designer needs to be aware of the necessary standards to which the product must adhere. These include: ATEX, IECEx and the UL/CSA approvals bodies, to name but a few.

Designers have to understand the nuances of each of these standards and while all are intended to achieve the safe specification, installation and operation of electrical equipment in hazardous areas, they are subtly different in principles, classification and approach.

In choosing a switch – and assuming the product meets the relevant local standard – a designer may also look for a device with particular features.

But whatever switch you choose, and whatever the environment, pick a manufacturer that you can trust with your life. Because in the world of hazardous environments, that is precisely what you may be doing.

• Leslie Neill is product manager for Honeywell Safety and Productivity Solutions