22nd November 2018
Hazardous Area Meters
Specifying the correct flow meter for use in areas with explosive atmospheres is complex and critical to get right from a safety and regulatory view. This Tech Corner defines what a hazardous area is, the types of hazard reduction philosophies available with Oval Gear meters and the factors that affect the choice of hazard reduction method. Installation of hazardous area meters and instrumentation should be undertaken by personnel authorised under local regulations. It is the customer’s responsibility to ensure that any hazardous area application complies with local safety regulations and installation of hazardous area meters and instrumentation should be undertaken by appropriately authorised personnel.
Using Oval Gear Meters In Explosive Atmospheres
Meters are often required in hazardous areas where there is a potential for an explosion if there is an ignition source. An explosive atmosphere is defined as a mix of flammable gas and air, where once the mixture is ignited the combustion spreads to the unburnt components. There are three conditions required to cause an explosion or fire as depicted by the Hazard Triangle. Hazardous area protection concepts seeks to remove one of the elements of the Hazard Triangle.
The Hazard Triangle
There are three components that have to be present for an explosion or fire to occur, which in system safety is known as the Hazard Triangle. The Triangle shows that a flammable hazard is comprised of three sides can also be termed as Fuel, Oxygen and Ignition Source.
Remove any side of the triangle and the hazard is reduced. Reducing the probability of the ignition source side for instance, and you also reduce the probability of a mishap (Intrinsic Safety). Reduce the energy or fuel source or the volume of oxygen that can fuel combustion as the other sides of the triangle and you reduce the severity of any mishap (Flameproof). This particular aspect of a hazard can help when you are trying to determine which hazard management strategy to employ.
What is Intrinsically Safe
An intrinsically safe philosophy limits the energy of equipment below the ignition point of the atmosphere. In other words, an intrinsically safe system has no potential spark or heat sources that could cause an explosion because all possible energy sources that could create ignition have been removed.
An Intrinsically Safe meter (I.S) may look identical to a regular meter, but operates differently by limiting the operating power and by using a simple apparatus sensor, the reed switch. A simple apparatus is a device that has a passive component such as a switch, junction box, resistor or that limit stored energy or output less than 1.5 V such as an LED. Intrinsically safe meters must be paired with Intrinsically Safe displays or totalisers as the energy storage of the whole system must be below a certain power limit.
What is Explosion Proof?
A Flame Proof or Explosion Proof protection concept contains any explosion to the ignition source (due to arcs, sparks or flashes) and prevents the transmission of the combustion outside of the equipment. Energy sources must be contained within enclosures that will be strong enough to withstand the pressures and temperatures created by an internal explosion and have gaps small enough that some hot gases can escape but the flame cannot.
Explosion proof meters appear externally different to a regular meter or an I.S meter. The meter cap changes from the standard Glass Reinforced Nylon (GRN) to either Stainless steel or Aluminium depending on the meter material and contains the potential ignition source of the meter board with a more robust and stronger material. The explosion proof meter will also require flameproof cable glands and cable for any electrical and signal connections, although the power limits are the same as a regular meter.
What does this mean for your meter selection?
Selecting either Explosion proof (EX-d) or Intrinsically Safe (I.S) does change how the meter is built and limits what displays can be used with the meter.
Both types of meters are suitable for hazardous areas however the intrinsically safe equipment is inherently safer than flame proof equipment as the energy in the system is not present for ignition and should be the preferred protection concept where possible. However sometimes explosion proof equipment is required for customer request or where a powered Hall Effect sensor is necessary such as quadrature pulse or pulsating flow options.
The safe operating design of hazardous area equipment is certified by a number of different bodies around the world. The customer and national legislation will determine which certification is required. Flomec oval gear meters have EXd and IS certification with ATEX and IECEX.
However when it comes to mechanical registers, there is no electrical energy as the entire assembly uses mechanical energy to drive the register.
UK Flowtechnik Ltd are the UK distributor to GPI flow meters for further application information, feel free to call one of our flow meter specialist on: 0115 901 7111 alternatively email: firstname.lastname@example.org