Page 214 - Electrical Installation in Hazardous Area

8

General requirements for explosion
protected apparatus (gas, vapour

and mist risks)

Apparatus to European Standards

Before embarking upon a detailed examination of the general requirements'
Standard it is necessary to understand the wording used in this and other
Standards. First, the Standard does not have the imperative of legislation
and cannot dictate what must or must not be done to comply with the law
in any country.
The words which are important in this and other Standards are, first shall,
the use of which indicates that a requirement is a necessity as far as the
Standard is concerned. If this is not complied with compliance with the
Standard cannot be claimed.
Second, the use of should, which indicates a strong recommendation but
allows some flexibility in application of the Standard. In other words, it may
be that, occasionally, an alternative approach producing the same effective
result will be acceptable. The stress here is on the word occasional as the
relaxation is not intended to allow a coach and horses to be driven through
the Standard. It should be noted that the word should is only occasionally
used in any event.
The word must is seldom used in Standards but where it does appear
it means that a law exists at the time the Standard was written, and an
imperative is appropriate. The Standard is not in this case making law but
drawing attention to the existence of law.
Chapter 7 identifies the European Standards which exist for the differing
types of explosion protected equipment. It draws attention to the fact that,
unlike the preceding National Standards in the UK where all of the require-
ments were contained within the particular protection concept Standard,
the European Standards contain only those requirements specific to the
particular protection concept, with the more general requirements (i.e., those
which applied to several of the protection concepts) being contained in a
general requirements' Standard to which the protection concept Standards
refer. The requirements of this Standard are then considered to apply to
all of the particular protection concept Standards, unless a particular Stan-
dard specifically excludes one or more of these general requirements. This
approach is considered to minimize the duplication of effort by the Stan-
dards writing committees and give a more rational approach. In practice,