SECTION 1 : INTRODUCTION

1.1 This Standard is issued as a Supplement to IGEM/TD/1 Edition 5, and
       supersedes IGEM/TD/1 Edition 5 Supplement 1 which is now obsolete.
       This Supplement 1 Edition 2 can be read and used independently of IGEM/TD/1.
       The advice contained herein may be used for the handling, transport and
       storage of steel components to be used in any fuel gas installation, such as
       those designed and installed in accordance with IGEM/TD/3, IGE/TD/4,
       IGEM/TD/13, IGEM/UP/2, IGEM/UP/3, IGEM/UP/6, IGE/UP/7, IGE/UP/9,
       IGEM/UP/10, IGEM/UP/11, IGEM/UP/12, IGEM/G/5, IGE/GM/4, IGEM/GM/6 and
       IGEM/GM/8 (see the list of all Standards available at www.igem.org.uk).
1.2  This Standard makes use of the terms “must”, “shall” and “should”, when
       prescribing particular requirements:
    •  the term “must” identifies a requirement by law in Great Britain (GB) at the
       time of publication
    •  the term “shall” prescribes a procedure which, it is intended, will be
       complied with in full and without deviation
    •  the term “should” prescribes a procedure which, it is intended, will be
       complied with unless, after prior consideration, deviation is considered to be
       acceptable.
1.3  This Standard has been drafted by a Panel appointed by the IGEM’s Gas
       Transmission and Distribution Committee, subsequently approved by that
       Committee and published by the authority of the Council of IGEM.
1.4  It is now widely accepted that the majority of accidents in industry generally are
       in some measure attributable to human as well as technical factors in the sense
       that actions by people initiated or contributed to the accidents, or people might
       have acted better to avert them.
       It is therefore necessary to give proper consideration to the management of
       these human factors and the control of risk. To assist in this, it is recommended
       that due cognisance should be taken of the publication HS(G)48.
1.5  The primary responsibility for compliance with legal duties rests with the
       employer. The fact that certain employees, for example “responsible engineers”,
       are allowed to exercise their professional judgement does not allow employers
       to abrogate their primary responsibilities. Employers must:
 (a) Have done everything to ensure, so far as is reasonably practicable, that
       there are no better protective measures that can be taken other than
       relying on the exercise of professional judgement by “responsible
       engineers”.
(b)  Have done everything to ensure, so far as is reasonably practicable, that
       “responsible engineers” have the skills, training, experience and personal
       qualities necessary for the proper exercise of professional judgement.
(c)  Have systems and procedures in place to ensure that the exercise of
       professional judgement by “responsible engineers” is subject to
       appropriate monitoring and review.

(d)  Not require “responsible engineers” to undertake tasks which would
       necessitate the exercise of professional judgement that is beyond their
       competence. There should be written procedures defining the extent to
       which “responsible engineers” can exercise their judgement. When
       “responsible engineers” are asked to undertake tasks that deviate from
       this, they should refer the matter for higher review.
1.6  This Standard does not attempt to make the use of any method or specification
       obligatory against the judgement of the responsible engineer. Where new and
       better techniques are developed and proved, they are to be adopted without
       waiting for modification to this Standard. Amendments to this Standard will be
       issued when necessary and their publication will be announced in the Journal of
       IGEM and other publications as appropriate.
1.7 Requests for interpretation of this Standard in relation to matters within its
       scope, but not precisely covered by the current text, should be addressed to
       Technical Services, IGEM, IGEM House, 26-28 High Street, Kegworth,
       DE74 2DA, email: [email protected] and will be submitted to the relevant
       Committee for consideration and advice, but in the context that the final
       responsibility is that of the engineer concerned. If any advice is given by or on
       behalf of IGEM, this does not relieve the responsible engineer of any of his or
       her obligations.
1.8  This Standard was published in July 2018.

IGEM/SR/25 Edition 2 (and Supplement 1 to IGEM/SR/25) complements BS EN 60079-10-1 by providing detailed requirements for the hazardous area classification of permanent and temporary Natural Gas, hydrogen or NG/H blend installations. A hazardous area is an area in which explosive gas/air mixtures are, or may be expected to be, present in quantities such as to require special precautions for the construction, installation and use of electrical apparatus or other sources of ignition.

The concept of Vz and a zone of negligible extent is only applicable in IGEM/SR/25 Edition 2 including supplement to:

• Natural Gas and NG/H Blend installations of MOP not exceeding 10 bar
• Hydrogen Installations of MOP not Exceeding 2 Bar.

This spreadsheet is based upon IGEM/SR/25 Edition 2 (and Supplement 1 to IGEM/SR/25) and applies to:

• Liquid-free Natural Gas with a combined proportion of methane-plus-inerts of greater than 89% by volume; a gross calorific value not exceeding 45 MJ m-3; molecular weight not exceeding 20 kg kmol-1; LFL of not less than 4.4%; gauge pressure not exceeding 100 bar. 
• Pure liquid-free hydrogen with gas quality specifications in accordance with IGEM/H/1; gauge pressure not exceeding 200 bar.
• Liquid-free 20% hydrogen / 80% natural gas by volume with gas quality specifications for hydrogen in accordance with IGEM/H/1 and gas quality specifications for natural gas in accordance with IGEM/SR/25; gauge pressure not exceeding 100 bar.

Gas temperature are assumed to be in a temperature range of –20°C to 50°C and Ambient temperatures are assumed to be in the range - 20°C to 35°C.

^{_{Note 1: This spreadsheet does not apply to either compressed or liquefied Natural Gas (CNG or LNG) vehicle filling station installations. Guidance on the latter is provided by the Energy Institute.}}

This spreadsheet is not intended for use by persons who are not familiar with IGEM/SR/25 – it is an aid to zoning to complement the standard and not a substitute for a full understanding of IGEM/SR/25 Edition 2 including supplement 1

Contents
Calculation of Zones and their extent in relation to:

1. Natural Gas installations in Buildings
2. Vents for Natural Gas installations
3. Gasholders
4. Natural Gas installations Outdoors