Intro4u2u

Flameproof Technique:
This technique is implemented by enclosing
all electrical circuits in housing
and conduits strong enough to contain
any explosion or fires that may take
place inside the apparatus.
Advantages of this Technique

Users are familiar with this technique
and understand its principles
and applications.

Sturdy housing designs provide
protection to the internal components
of the apparatus and allow their application
in hazardous environments.

A flameproof housing is usually
weatherproof as well.
Disadvantages of this Technique

Circuits must be de-energized or
location rendered nonhazardous before
housing covers may be removed.

Opening of the housing in a hazardous
area voids all protection.

This technique generally requires
use of heavy bolted or screwed
enclosures.
Increased Safety Technique:
The increased safety technique incorporates
special measures to reduce
the probability of excessive temperatures
and the occurrence of arcs or
sparks in normal service.
Chapter 9. Standards and Approvals
189
Advantages of this Technique

Increased safety enclosures provide
at least IP54 enclosure protection.

Installation and maintenance are
easier for flameproof enclosures.

This technique offers significantly
reduced wiring costs over flameproof
installations.
Disadvantages of this Technique

This technique is limited in the
apparatus for which it may be used. It
is normally used for apparatus such
as terminal boxes and compartments.
Intrinsically Safe Technique:
This technique requires the use of intrinsically
safe barriers to limit the current
and voltage between the hazardous
and safe areas to avoid the
development of sparks or hot spots in
the circuitry of the instrument under
fault conditions.
Advantages of this Technique

This technique costs less because
of less stringent rules for field
wiring of the apparatus.

Greater flexibility is offered because
this technique permits simple
components such as switches, contact
closures, thermocouples, RTD’s,
and other non-energy-storing apparatus
to be used without special certification
but with appropriate barriers.

Ease of field maintenance and
repair characterize this technique.
There is no need to remove power before
adjustments or calibration are
performed on the field instrument. The
system remains safe even if the instrument
is damaged, because the
energy level is too low to ignite