Consulenza Direttiva ATEX

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.

Where electrical

equipment has to be used in these areas it must be so

designed and constructed as to not create sources of ignition

capable of igniting these mixtures.

Before electrical

equipment can be used in a potentially explosive atmosphere

a representative sample has to be fully tested and certified

by an independent authority such as BASEEFA in the U.K.

or UL in the U.S.A.

This information

is intended as a guide only and further expert guidance

should be sought before placing into service, maintaining

or repairing any item of equipment in a Potentially Explosive

Atmosphere.

Where comparisons

are shown between, for example, European and North American

practice this may be an approximation and individual standards/codes

of practice should be consulted for precise details.

MEDC have spent 25 years
designing and manufacturing electrical equipment suitable
for use in potentially explosive atmospheres. We deal with
all the major testing and certification authorities throughout
the world and have a diverse range of internationally approved
products..

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.

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.

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

Temperature

e.g. Butane has an

ignition temperature of 365 degrees Centigrade, equipment

used in the vicinity of this gas would need a T rating

of T2 or higher.

Types of Electrical Equipment Suitable for

use
in Potentially Explosive Atmospheres

Different techniques

are used to prevent electrical equipment from igniting

explosive atmospheres. There are restrictions on where

these different types of equipment can be used as follows

:

Selection, Installation and Maintenance of Electrical Equipment
Intended for use in
Potentially Explosive
Atmospheres

All Explosion-proof electrical
equipment is maintained, by suitably trained personnel, in accordance
with the Manufacturers' recommendations.

Any spare parts used

should be purchased from the original Manufacturer and

repairs should be carried out by the Manufacturer or under

his supervision, in order that the item remains in conformance

with the certification documents.

The Certification Process

All Electrical Equipment,

intended for use in a Potentially Explosive Atmosphere,

should be certified as suitable for such use.

The methods of obtaining

certification differ in detail, see below, between each

certifying body or group of bodies (e.g. CENELEC). Basically

this process consists of supplying a representative sample

of the equipment along with a set of drawings to a recognised

test/certification body e.g. BASEEFA who in turn test

the equipment against a recognised Standard e.g. EN50018

and issue a Certificate. The user of the equipment can

then refer to this Certificate to enable him to safely

put the item into service in a zone appropriate to the

Certification.

European
Practice – after 1st July 2003

After the above date

the ATEX Directive comes into force throughout

the EEC. This becomes a mandatory requirement for all

equipment intended for use in a hazardous area. The fundamental

difference between current practice 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.

ALL EQUIPMENT,

BOTH ELECTRICAL AND MECHANICAL, INTENDED TO BE PUT INTO

SERVICE WITHIN THE EEC AFTER 1ST July 2003, WILL HAVE

TO HAVE BEEN CERTIFIED IN ACCORDANCE WITH THE ATEX DIRECTIVE.

In practice this

means re-certification of all currently certified electrical

equipment.

MEDC have

started this process and all relevant equipment will be

covered by the implementation date of 1st July 2003.

It should be noted

also that MECHANICAL equipment is covered by the

ATEX Directive so for the first time items such as gearboxes

will have to carry ATEX certification.

The equipment coding

will be as the current practice plus an additional code

as follows:

ExII2G i.e.

Ex – Explosion

proof in accordance with ATEX.

II – Group II

surface industries.

G – suitable

for atmospheres containing gas ( D is suitable for atmospheres

containing dusts).

Equipment will be
CE marked when certified to ATEX.

European Practice
– Current – until 30th June 2003

The method is basically
as above. In addition all electrical equipment intended
for use in the European Economic Community (EEC) must
comply with Electromagnetic Compatibility regulations
(EMC) and manufacturers must issue, on request, an EC
Declaration of Conformity in accordance with the EMC regulations.

When certified, an
item of equipment and its' certificate, carry a code e.g.
EExdIIBT4. This can be broken down as follows:

E – European
certificate in accordance with harmonised 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).

North American
Practice

Sample equipment
and supporting documentation are submitted to the appropriate
authority e.g. .U.L., F.M., C.S.A.

The equipment is
tested in accordance with relevant standards for explosion
protection and also for general electrical requirements
e.g. light fittings.

After successful
testing a listing is issued allowing the manufacturer
to place the product on the market.

The product is marked
with the certification details such as the gas groups
A,B,C,D the area of use e.g. Class 1 Division 1

World-wide Certification

Most countries outside

Europe or North America use the IEC Standards as a basis

for their own national standards.

The Russian Federation certifies
equipment to GOST
standards, these closely follow CENELEC practice.

There is a scheme

in place which will when fully adopted allow for internationally

recognised certification to become a reality, this is

the IEC EX SCHEME. This uses the IEC standards and IEC

recognised test and certification bodies to issue mutually

recognised test reports and certificates. The scheme is

in its infancy and its level of success cannot yet be

measured.

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)