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.
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.
2
– category 2 equipment (suitable
.....for use in Zone
1) note: |
Category 1 is suitable for Zone 0. |
|
Category
3 is suitable for Zone 2. |
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)
| . |
Solids |
. |
Liquids |
| 0 |
No
protection.
|
0 |
No
protection.
|
| 1 |
Protected
against solid objects
up to 50mm, e.g. hands. |
1 |
Protected
against vertically falling
drops of water. |
| 2 |
Protected
against solid objects
up to 12mm, e.g. fingers. |
2 |
Protected
against water spray up
to 15 degrees from vertical. |
| 3 |
Protected
against solid objects
up to 2.5mm, e.g. tools. |
3 |
Protected
against water spray up to
60 degrees from vertical. |
| 4 |
Protected
against solid objects
over 1mm, e.g. wires. |
4 |
Protected
against water sprays from
all directions. |
| 5 |
Protected
against dusts.
(No harmful deposits). |
5 |
Protected
against water jets from
all directions. |
| 6 |
Totally
protected against dust.
|
6 |
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. |
