FAQ

Potentially Explosive Atmospheres exist where there is a risk of explosion due to mixtures of gas/air, vapor/air, dust/air or other flammable combinations. In such areas there is a necessity to eliminate sources of ignition such as sparks, hot surfaces or static electricity which may ignite these mixtures.

Process plants are divided into Zones (European and IEC method) or Divisions (North American method) according to the likelihood of a potentially explosive atmosphere being present.

Note : North American legislation now allows Zones to be used to classify areas, where this practice is used it follows the IEC Zone method.

Zone 0 (gases)
Zone 20 (dusts)

An area in which an explosive mixture is continuously present or present for long periods

Class I Division 1 (gases)
Class II Division 1 (dusts)

Zone 1 (gases)
Zone 21 (dusts)

An area in which an explosive mixture is likely to occur in normal operation

Class I Division 1 (gases)
Class II Division 1 (dusts)

Zone 2 (gases)
Zone 22 (dusts)

An area in which an explosive mixture is not likely to occur in normal operation and if it occurs it will exist only for a short time

Class I Division 1 (gases)
Class II Division 1 (dusts)
Class III Division 1 (fibres)
Class III Division 2 (fibres)

There are two main gas groups, Group I – Mining only and Group II – Surface Industries These categories are used in European and I.E.C. groupings. Group I is concerned only with underground mining where methane and coal dust are present. Group II gases occurring in surface industries, are sub-grouped according to their volatility. This enables electrical equipment to be designed to less onerous tolerances if it is to be used with the least volatile gases.

Methane

I

-

Acetylene

IIC

A

Hydrogen

IIC

B

Ethylene

IIB

C

Propane

IIA

D

Metal dust

-

E

Coal dust

-

F

Grain dust

-

G

EExdIIBT4. This can be expanded as follows:

E – European certificate in accordance with harmonized standards

Ex – Explosion-proof electrical equipment

d – flameproof enclosure type of protection

II – Group II surface industries

B – gas group B

T4 – temperature class T4 (135 degrees centigrade surface temperature)

IP means ingress protection i.e. protection of apparatus from the entry of solids / liquids.

Ingress Protection

2 digits are used to denote the level of ingress protection that a piece of apparatus enjoys :– (The first digit denotes the level of protection against solid objects and the second against liquids)

0

No protection.

No protection.

1

Protected against solid objects up to 50mm, e.g. hands.

Protected against vertically falling drops of water.

2

Protected against solid objects up to 12mm, e.g. fingers.

Protected against water spray up to 15 degrees from vertical.

3

Protected against solid objects up to 2.5mm, e.g. tools.

Protected against water spray up to 60 degrees from vertical.

4

Protected against solid objects over 1mm, e.g. wires.

Protected against water sprays from all directions.

5

Protected against dusts. (No harmful deposits).

Protected against water jets from all directions.

6

Totally protected against dust.

Protected against strong water jets from all directions, e.g. Offshore.

7

-

Protected against immersion between 15cm and 1m in depth.

8

-

Protected against long immersion under pressure.

ATEX has been initiated by the European Countries, and has come into force as a directive since 1st July 2003 throughout the EEC.

This becomes a mandatory requirement for all equipment intended for use in a hazardous area. The fundamental difference between regular approvals and ATEX certification is that ATEX addresses the essential safety requirements for hazardous area equipment and uses Standards as part of the method of conforming to these. Amongst other documentation required by certifying authorities will be Technical Manuals in order that the user is informed of installation methods etc.

NEMA is the Acronym for National Electrical Manufacturers’ Association

North American practice is to use NEMA standards to describe ingress protection, i.e.:

The ignition temperature is the lowest temperature on the surface at which an explosive atmosphere will ignite. Gases and dusts have been divided into temperature classes according to their ignition temperatures so that electrical equipment can be further sub-divided into six temperature classes T1 to T6. The temperature classes are shown in Table 5.

Note. The maximum operating surface temperature of a piece of electrical equipment must always be below the ignition temperature of the explosive mixture, see Table 6 below.

India: PESO – ( Petroleum and Explosives Safety Organization – Nagpur ) This is headed by the Chief Controller of Explosives whose approval is mandatory for the use of Ex equipment in India especially for IIA & IIC gas groups. Generally the approval is issued after verification of the test report whether from India or abroad.

All equipments operating on electrical energy are required to be approved by Chief Controller of Explosives if they find application in hazardous areas falling within the purview of Petroleum Rules, 2002. The approval of electrical equipment is therefore limited to only such areas falling within the jurisdiction of Petroleum & Explosives Safety Organisation.

Orifice Plate is used to measure the flow in the pipe line through Dp transmitter whereas Restriction orifice plate is used to reduce the flow pressure in the pipe line.

Upstream & Downstream tapping distance is 25.4 mm respectively, from the center of the tapping point to the upstream face of the orifice plate.

Vent hole will be provided for liquid services and drain hole will be provided for gas and vapour services.

Yes, gasket thickness is included in the tapping distance.

For these kind of Flanges, carrier rings are to be provided on both sides of the orifice plate and tappings to be done on the carrier rings.

Generally Flow nozzles are used in high pressure and high temperature lines.

Normally Venturi Tube is used for very low pressure applications.

Multistage restriction orifice is used to drop high pressure at different stages.

No, Multistage is designed only as per manufacturing standard.

In India, for all steam applications and boiler feed water applications, IBR Certification is must for material.

For Hydrogen service (H2) and HIC + Sour applications, NACE certification is required for the material.

Yes, it is possible to calibrate the Flow Elements (Orifice, Nozzle & Venturi). Calibration is carried out at Fluid Control Research Institute, Palghat and IIT, New Delhi.

The Crimping of PVC seals over the LPG cylinder valves using hot air, is done by the aid of the Hot air sealing system in the hazardous location classified as Zone 1 & 2, Group IIA & IIB.

The benefits are many :
(a) Quality & Tamper proof sealing
( b) Seal cost reduced compared with Aluminium seals
(c) Reduced manpower cost by means of automated equipment
(d) maintenance cost is cut down due to Pre Engineering of the equipment.

There are 4 models of automated HASM available, to suit various production rates. Further portable OR Manually operated model HASM also is available to use in Quality check points and near to cylinder loading points.

The inputs required for designing the HASM are LPG cylinder dimensions and details , valve dimensions, conveyor speed and production rate.

In the automatic system, 1 No. RTD + Temperature controller and 1 No. thermostat are used as redundant temperature control. In the Portable system, 1 No. Thermostat and 1 No. Thermal fuse are used as redundant control.

A totalizing counter is provided in automated systems to count sealed cylinders that exit from the machine.

Yes, it is possible by means of a common sealing system with mix & match feature.