Bsi bs en 60079 13 2010

3.23 type of protection py pressurization that allows for the required Gb equipment protection level EPL within the pressurized room to be reduced to Gc by maintaining an internal over

BSI Standards Publication

Explosive atmospheres

Part 13: Equipment protection by pressurized room “p”

A list of organizations represented on this committee can be obtained onrequest to its secretary.

This publication does not purport to include all the necessary provisions of acontract Users are responsible for its correct application

© BSI 2011ISBN 978 0 580 60924 4ICS 29.260.20

Compliance with a British Standard cannot confer immunity from legal obligations.

This British Standard was published under the authority of the StandardsPolicy and Strategy Committee on 31 May 2011

Amendments issued since publication Amd No Date Text affected

NORME EUROPÉENNE

CENELEC

Management Centre: Avenue Marnix 17, B - 1000 Brussels

© 2010 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members

Ref No EN 60079-13:2010 E

ICS 29.260.20

English version

Explosive atmospheres - Part 13: Equipment protection by pressurized room "p"

This European Standard was approved by CENELEC on 2010-12-01 CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration

Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENELEC member

This European Standard exists in three official versions (English, French, German) A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified

to the Central Secretariat has the same status as the official versions

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom

Foreword

The text of document 31/878/FDIS, future edition 1 of IEC 60079-13, prepared by IEC TC 31, Equipment for explosive atmospheres, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 60079-13 on 2010-12-01

This part of EN 60079 is to be read in conjunction with EN 60079-0

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights CEN and CENELEC shall not be held responsible for identifying any or all such patent rights

The following dates were fixed:

– latest date by which the EN has to be implemented

at national level by publication of an identical

national standard or by endorsement (dop) 2011-09-01

– latest date by which the national standards conflicting

with the EN have to be withdrawn (dow) 2013-12-01

Annex ZA has been added by CENELEC

Endorsement notice

The text of the International Standard IEC 60079-13:2010 was approved by CENELEC as a European Standard without any modification

In the official version, for Bibliography, the following notes have to be added for the standards indicated:

IEC 60079-17 NOTE Harmonized as EN 60079-17

IEC 60079-20-1 NOTE Harmonized as EN 60079-20-1

IEC 60079-29 series NOTE Harmonized in EN 60079-29 series (partially modified)

IEC 60529 NOTE Harmonized as EN 60529

IEC 61285 NOTE Harmonized as EN 61285

IEC 61511 series NOTE Harmonized in EN 61511 series (not modified)

Annex ZA

(normative)

Normative references to international publications with their corresponding European publications

The following referenced documents are indispensable for the application of this document For dated

references, only the edition cited applies For undated references, the latest edition of the referenced

document (including any amendments) applies

IEC 60050-426 - International Electrotechnical Vocabulary -

Part 426: Equipment for explosive atmospheres

- -

IEC 60079-0 - Explosive atmospheres -

Part 0: Equipment - General requirements EN 60079-0 -

IEC 60079-2 - Explosive atmospheres -

Part 2: Equipment protection by pressurized enclosure "p"

EN 60079-2 -

IEC 60079-10-1 - Explosive atmospheres -

Part 10-1: Classification of areas - Explosive gas atmospheres

EN 60079-10-1 -

IEC 60695-11-10 - Fire hazard testing -

Part 11-10: Test flames - 50 W horizontal and vertical flame test methods

EN 60695-11-10 -

CONTENTS

1 Scope 7

2 Normative references 10

3 Terms and definitions 10

4 Requirements for rooms 13

4.1 General 13

4.2 Construction 13

4.3 Mechanical strength 14

4.4 Openings, penetrations and seals 14

4.5 Doors 14

4.6 Inlets and outlets 14

4.7 Ducts 14

5 Clean air supply 14

5.1 Source of clean air 14

5.2 Environmental and air temperature conditions 15

5.3 Heating, ventilation and air conditioning services 15

5.4 Minimum flow rate 15

6 Purging and cleaning 15

6.1 General 15

6.2 Gases – Purging 15

6.2.1 General 15

6.2.2 Purge volume 15

6.2.3 Purging flow rate 15

6.2.4 Sequence of operations of the purging safety devices for type of protection px 16

6.2.5 Enclosures within the room 16

6.3 Dusts – Cleaning 16

7 Temperature limits 16

8 Minimum safety provisions, safety devices and electrical disconnects 16

8.1 Safety devices 16

8.2 Safety devices based upon type of protection 17

8.3 Gas detectors 18

8.4 Failure of the pressurization system 18

9 Pressurized room in a hazardous area and with no internal source of flammable substance 18

9.1 General 18

9.2 Protective gas 18

9.2.1 Type of protection px 18

9.2.2 Type of protection py 18

9.2.3 Type of protection pz 19

9.3 Pressurization system 19

9.3.1 Room pressure differential 19

9.3.2 Power for pressurization system 19

9.4 Preventing the explosive atmosphere from entering an open door 19

9.5 Airlock 19

9.6 Outward air velocity through a door 20

9.7 Air consuming device 20

9.8 Action when pressurization system fails 20

9.8.1 Type of protection px 20

9.8.2 Types of protection py and pz 20

9.9 Re-energizing the room 21

10 Pressurized room in a hazardous area and containing an internal source of flammable substance 21

10.1 Evaluation of internal sources of a flammable substance 21

10.1.1 Flammable substance assessment 21

10.1.2 Assessment of release 21

10.1.3 Release – Additional requirements 21

10.1.4 Adequate dilution 21

10.2 Applicability of Clause 9 21

10.3 Containment system 21

10.4 Sample lines 21

10.5 Types of anticipated releases 22

10.5.1 General 22

10.5.2 No release 22

10.5.3 Negligible release 22

10.5.4 Limited release 22

10.5.5 Unlimited release 22

10.6 Safety measures 23

10.7 Minimum flow rate for dilution 23

10.8 Warning to prevent entry into a room 25

10.9 Air distribution 25

10.10Protective gas 25

10.11Additional pressurization system requirements when inert gas is used 25

11 Pressurized room in a non-hazardous area with internal source of flammable substance (type of protection pv) 25

11.1 Applicability of Clause 9 26

11.2 Applicability of Clause 10 26

11.3 Loss of flow of the protective gas 26

11.4 Safety devices 26

12 Verification 26

12.1 General 26

12.2 Sequence of tests 26

12.3 Mechanical strength test 26

12.4 Overpressure test 27

12.5 Purging test 27

12.6 Minimum pressure differential test for types of protection px, py and pz 27

12.7 Minimum flow rate test 27

12.8 Overpressure test for containment systems with limited release 27

12.9 Confirmation of the ratings of the safety devices 27

12.10Verification sequence of operation of the safety devices 27

13 Marking 28

14 Technical documentation 28

Annex A (normative) Containment system 30

Annex B (informative) Maintenance 33

Annex C (informative) Guidelines when pressurization not immediately restored 34

Annex D (normative) Classification of the type of release within rooms 35

Bibliography 37

Table 1 – Exclusion of specific clauses of IEC 60079-0 8

Table 2 – Safety devices based on type of protection 17

Table 3 – Safety devices, loss of pressurization or use of inert protective gas 24

Table 4 – Protective gas requirements for a pressurized room with an internal flammable substance 25

EXPLOSIVE ATMOSPHERES – Part 13: Equipment protection by pressurized room “p”

A room may be a single room, multiple rooms, a complete building or a room contained within

a building and includes inlet and outlet ducts This part of IEC 60079 also includes requirements for associated equipment, safety devices and controls necessary to ensure that pressurization is established and maintained

This part of IEC 60079 covers rooms or buildings that are constructed or assembled on site, which may be either on land or off-shore, designed to facilitate the entry of personnel and primarily intended for installation by an end-user and verification on site The room may be located in an explosive gas atmosphere or a explosive dust atmosphere requiring equipment protection levels (EPL) Gb, Db, Gc or Dc

This part of IEC 60079 does not specify the methods that may be required to ensure adequate air quality for personnel with regard to toxicity and temperature within the room

NOTE 1 Whilst the scope of this part of IEC 60079 does not address toxicity it is vital that proper consideration is given to this aspect to ensure the safety of personnel National regulations and requirements should be observed

in this regard

NOTE 2 There is a related standard IEC60079-2 (Equipment protection by pressurized enclosure) covering the different conditions encountered when using the pressurization technique

NOTE 3 Maintenance needs are contained in Annex B until they are included IEC 60079-17

NOTE 4 For the purposes of this part of IEC 60079, the terms "lower flammable limit (LFL)" and "lower explosive limit (LEL)" are deemed to be synonymous, and likewise the terms "upper flammable limit (UFL)" and "upper explosive limit (UEL)" are deemed to be synonymous For ease of reference, the two abbreviations LFL and UFL may be used hereinafter to denote these two sets of terms It should be recognized that particular authorities having jurisdiction may have overriding requirements that dictate the use of one of these sets of terms and not the other

This part of IEC 60079 supplements and modifies the general requirements of IEC 60079-0, except as indicated in Table 1 Where a requirement of this standard conflicts with a requirement of IEC 60079-0, the requirement of this standard takes precedence

Table 1 – Exclusion of specific clauses of IEC 60079-0

Clause of IEC 60079-0

Ed 4.0 (2004) (Informative)

Ed 5.0 (2007) (Informative)

Clause / subclause title (Normative)

4.4 4.4 Equipment for a particular explosive

atmosphere

Applies 5.1 5.1 Environmental influences Applies 5.1.1 5.1.1 Ambient temperature Applies

5.1.2 5.1.2 External source of heating or cooling Applies

5.2 5.2 Service temperature Applies

5.3.1 5.3.1 Determination of maximum surface

temperature

Applies 5.3.2.1 5.3.2.1 Group I electrical equipment Applies

5.3.2.2 5.3.2.2 Group II electrical equipment Applies

5.3.2.3 5.3.2.3 Group III electrical equipment Applies

5.3.3 5.3.3 Small component temperature for

Group I and Group II electrical equipment

Applies

6.4 6.4 Circulating currents Excluded

6.5 6.5 Gasket retention Excluded

6.6 6.6 Electromagnetic and ultrasonic

16 16 Entries into enclosures Excluded

17 17 Supplementary requirements for

rotating electrical machines

Clause of IEC 60079-0

Ed 4.0 (2004) (Informative)

Ed 5.0 (2007) (Informative)

Clause / subclause title (Normative)

20 20 Supplementary requirements for plugs

22 22 Supplementary requirements for

caplights and handlights

25 25 Compliance of prototype or sample

with documents Excluded

28 28 Manufacturers responsibility Applies

NR 29.6 Multiple types of protection Applies

NR 29.7 Ga using two independent Gb types of

29.7 29.10 Extremely small equipment and

extremely small Ex components Excluded 29.8 29.11 Warning markings Applies

NR 29.12 Alternate marking of equipment

protection levels (EPLs)

Applies 29.9 29.13 Cells and batteries Excluded

29.10 29.14 Examples of marking Applies

Annex A Annex A Supplementary requirements for Ex

cable glands

Excluded Annex B Annex B Requirements for Ex components Excluded

Annex C Annex C Example of rig for resistance to impact

NR Annex D Introduction to an alternative risk

assessment method encompassing

“equipment protection levels” for Ex equipment

Applies

Applies – This requirement of IEC 60079-0 is applied without change

Excluded – This requirement of IEC 60079-0 does not apply

Clause of IEC 60079-0

Ed 4.0 (2004) (Informative)

Ed 5.0 (2007) (Informative)

Clause / subclause title (Normative)

NOTE The applicable requirements of IEC 60079-0 are identified by the clause title

which is normative This table was written against the specific requirements of

IEC 60079-0, Ed 6.0 The clause numbers for the 6 th and previous edition are shown

for information only This is to enable the General Requirements IEC 60079-0, Ed 5.0,

to be used where necessary with this part of IEC 60079 Where there were no

requirements for the 5 th edition but there are for the 6 th edition (indicated by NR

against the 5 th edition only), or where is a conflict between requirements, the 6th

edition requirements should be considered

2 Normative references

The following referenced documents are indispensable for the application of this document For dated references, only the edition cited applies For undated references, the latest edition

of the referenced document (including any amendments) applies

IEC 60050(426), International Electrotechnical Vocabulary – Part 426: Equipment for

explosive atmospheres

IEC 60079-0, Explosive atmospheres – Part 0: Equipment – General requirements

IEC 60079-2, Explosive atmospheres – Part 2: Equipment protection by pressurized enclosure

“p”

IEC 60079-10-1, Explosive atmospheres – Part 10-1: Classification of areas – Explosive gas

atmospheres

IEC 60695-11-10, Fire hazard testing – Part 11-10: Test flames – 50 W horizontal and vertical

flame test methods

3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 60050(426) and IEC 60079-0 as well as the following terms and definitions apply

NOTE Unless otherwise specified, the terms “voltage” and “current” mean the r.m.s values of an alternating, direct or composite voltage or current

internal source of flammable substance

point or location from which a flammable substance may be released into the room or building such that an explosive gas atmosphere could be formed

NOTE This is also known as Upper Explosive Limit (UEL)

NOTE Pressurization as used in this part of IEC 60079 applies to a room

volume of the empty room

NOTE The term “room” is employed without distinction to designate rooms, groups of rooms or buildings

3.23

type of protection py

pressurization that allows for the required Gb equipment protection level (EPL) within the pressurized room to be reduced to Gc by maintaining an internal overpressure and diluting when there is an internal source of release

3.24

type of protection pz

pressurization that allows for the required Gc or Dc equipment protection level (EPL) within the pressurized room to be reduced to none by maintaining an internal overpressure and diluting when there is an internal source of release

Type of protection px allows for the required Gb or Db equipment protection level (EPL) within the pressurized room to be reduced to permit the use of non-explosion protected equipment

by maintaining an internal overpressure and diluting when there is an internal source of release

NOTE 1 This permits unprotected equipment to be installed within the pressurized room except for pressurization

defined safety devices (see 8.1)

NOTE 2 Because type of protection px reduces the EPL to none (a nondefined EPL) there are more onerous requirements concerning its application with respect to interlocks, alarms, etc

Type of protection py allows for the required Gb equipment protection level (EPL) within the pressurized room to be reduced to Gc by maintaining an internal overpressure and diluting when there is an internal source of release,

NOTE 3 For pressurization defined safety devices (see 8.1).

Type of protection pz allows for the required Gc or Dc equipment protection level (EPL) within the pressurized room to be reduced to permit the use of non-explosion protected equipment

by maintaining an internal overpressure and diluting when there is an internal source of release

NOTE 4 This permits unprotected equipment to be installed within the pressurized room except for pressurization defined safety devices (see 8.1)

Type of protection pv is in essence protection by dilution, and allows for the required Gb or

Gc equipment protection level (EPL) within the pressurized room to be reduced to, permit the use of non-explosion protected equipment where there is only an internal source of release and the pressurized room is located in an non-hazardous area

4.3 Mechanical strength

The room and any ducts and their connecting parts shall be designed to withstand the maximum pressure of the pressurization system This shall be verified by the design documentation or by the overpressure test of 12.3

The room, including windows, shall withstand the mechanical strength test of 12.3

NOTE Test for mechanical strength need not be carried out on the completed room but may instead be applied to all parts such as windows, gland plates, penetrations, doors, inlets or outlets of the room which are not made of steel or concrete but which are integral to the type of protection In which case the tests may be carried out on the parts themselves, appropriately mounted for the test

4.4 Openings, penetrations and seals

The entry of cables, electrical conduits and other penetrations into the room shall be sealed

so that the necessary pressure differential can be maintained

If floor drainage facilities are provided, measures shall be taken to minimize the exchange of atmosphere between the inside and the outside of the room

NOTE Barriers may need to be considered for certain room designs to prevent ingress of gases or vapours from potential external sources at atmospheric pressure

4.6 Inlets and outlets

The location of inlets and outlets shall be arranged to ensure even distribution of the clean air flow so as to avoid pockets where gases or vapours could accumulate, taking into account the density of those gases and vapours Design parameters and constraints shall be documented Exterior air intakes and outlets shall be arranged to minimize the effect of outside conditions

5 Clean air supply

5.1 Source of clean air

The source of the clean air shall be determined from the nature of the process and the physical layout and shall be preferably from a non-hazardous area Under certain conditions

as prescribed in 9.2, the source may be from a Zone 2 hazardous area

5.2 Environmental and air temperature conditions

The appropriate environmental and air temperature conditions for design as determined at the inlet to the room shall be documented

5.3 Heating, ventilation and air conditioning services

The clean air supply may include heating, ventilation, and air conditioning equipment Any outdoor air used by heating, ventilation and air conditioning equipment shall be provided from the clean air supply

NOTE Inlet filtering should be considered where conditions of dust, smoke, toxics or corrosive vapours or fumes may exist

5.4 Minimum flow rate

The continuous flow of clean air through the room shall be a minimum of 5 air changes per hour This may need to be increased for an air consuming device in accordance with 9.7 and where dilution is necessary in accordance with 10.7

6 Purging and cleaning

The pressurized room shall be purged by clean air, except where otherwise permitted or required by this part of IEC 60079

NOTE For example, see 10.11

6.2.2 Purge volume

The purge volume shall be a minimum of 10 room volumes unless a reduced purge volume can be verified by 12.5 or determined from criteria, such as that defined in IEC 60079-2

6.2.3 Purging flow rate

The purging flow rate shall be a minimum of 5 air changes per hour

The flow rate shall be monitored Verification shall be according to 12.7

If the room has a dedicated outlet, the flow shall be monitored at the outlet Where there is not a dedicated outlet, gas detectors shall be used to ensure that the air within the room is at

or below 25 % of the limiting value

6.2.4 Sequence of operations of the purging safety devices for type of protection px

The sequence of operations of the safety devices shall be as follows:

a) Following the initiation of the sequence, the purging flow through and the pressure differential between the internals of the room and the external atmosphere shall be monitored in accordance with this part of IEC 60079

b) The purge timer shall start once the minimum specified purging flow rate through the room

is verified and the pressure differential is within the specified limits

c) When the purge time has elapsed, the purging flow rate may be reduced to the level sufficient to maintain the required positive pressure in the room At that point, the equipment is permitted to be energised

In the event of failure of any step in the sequence, the purging cycle shall be restarted except

6.2.5 Enclosures within the room

During purging of the room, any enclosure which exceeds 5 % of the internal volume of the room and that contains electrical equipment not suitable for the equipment protection level external to the room, shall either be vented to the room so as to facilitate flow into and out of the enclosure or be individually purged

NOTE Top and bottom vents providing not less than 1 cm 2 of vent area for each 1 000 cm 3 with a minimum vent size of 6,3 mm diameter should be sufficient for adequate purging

6.3 Dusts – Cleaning

Before energizing any electrical equipment which is not suitable for the equipment protection level external to the room, excessive quantities of combustible dust shall be removed from the room and its contents

7 Temperature limits

Upon failure of the pressurization system, appropriate measures shall be taken to prevent the explosive atmosphere coming into contact with any hot surface within the room that exceeds the value documented in 14.1

NOTE This may be achieved by the design and construction of the room, (e.g air locks) or by bringing auxiliary ventilation systems into operation or by arranging that the hot surface within the room is in a gas tight or encapsulated housing

8 Minimum safety provisions, safety devices and electrical disconnects

NOTE 1 All parts of the system in contact with the room, including inside the inlet duct should be considered as being in the hazardous area

The safety devices shall be used within their normal operational limits

Alarms shall be located where they will immediately be perceived by the responsible personnel

The safety devices required by this part of IEC 60079 form safety-related parts of a control system

The safety and integrity of the control system shall meet a level of reliability consistent with the fault tolerance required for the relevant types of protection, i.e

– for type of protection px, or type of protection py, a single fault;

– for type of protection pz, normal operation;

– for type of protection pv, single fault

NOTE 2 For the integrity of safety functions IEC 61511 series or similar standards may be used

Electrical power disconnection to the room should preferably be in a non-hazardous area

8.2 Safety devices based upon type of protection

See Table 2 for required safety devices for each type of protection

Table 2 – Safety devices based on type of protection Design criteria Type of protection

None Pressure sensor or

flow sensor (see 9.8)

Pressure sensor or flow sensor (see 9.8)

Pressure sensor or flow sensor (see 9.8)

Time and flow marked

Time and flow marked Device for doors None Switch (see Clause 4) None None

None Gas detector, when an

airlock used without continuous flow (see 9.5)

Gas detector, when

an airlock used without continuous flow (see 9.5)

Gas Detector, if air intake in Zone 2 area (see 9.2.3)

Shut down

device(s)

Manual Valves to shut off flow

of flammable substance Valve to shut off an open flame (see Table 3)

Contacts to disconnect power (see Table 3)

Manual Manual

Device to permit

delayed shutdown

None Optional door switch or

gas detector (see 9.8.1)

Alarm (see 8.3) Alarm (see 8.3) Alarm (see 8.3) Alarm (see 8.3)

None = no additional safety device required

8.3 Gas detectors

The type, quantity and placement of detectors installed shall be based upon an end-user process risk evaluation and the specific IEC standards for gas detection (e.g IEC 60079-29 series)

NOTE The safety requirements resulting from the risk assessment may be fulfilled by documented proven-in-use apparatus

a) In those conditions when an asphyxiant hazard may be present, considerations shall be given towards the installation of a detection system within the room that can respond to appropriate safe gas levels in the room air with sufficient sensitivity, speed, and reliability (failure alarm, redundancy), and that can report any excursion above or below the designated concentration limit Gas alarms shall be arranged to alarm both locally and at

an attended location

b) If the gas detector requires a specified oxygen concentration for accurate operation, then

an oxygen analyzer, not subject to a common mode failure with the gas detector, is required and arranged to alarm both locally and at an attended location

c) Any oxygen gas monitor, if used, shall be arranged to locally alarm, both audibly and visually, at 19,5 % oxygen

8.4 Failure of the pressurization system

Failure of the pressurization system shall be determined by loss of clean air flow or by pressure differential below 25 Pa

NOTE Unless an airlock is used, the pressure differential may be lost when a door is opened and this may result

in unnecessary alarms Detecting clean air flow does not result in these alarms

Loss of the clean air flow shall be detected at the discharge end of the fan and shall activate

an alarm locally and at an attended location

Loss of pressure differential shall be detected by a sensor located in the room and shall activate an alarm locally and at an attended location

9 Pressurized room in a hazardous area and with no internal source of

no more than trace amounts of flammable vapour or gas under normal operating conditions

NOTE For safety of persons working within the room, at least one combustible gas detector with alarm in the air intake is recommended

a) There shall be at least one combustible gas detector with alarm in the air intake

b) There shall be at least one combustible gas detector with alarm within the room

c) Gas detection in the air intake shall be arranged to shutdown the intake of air containing flammable vapour or gas into the room on detection of 40 % of the limiting value

d) Detection and all other electrical equipment used for alarming and emergency actions/interlocks shall have an equipment protection level of Ga or Gb

9.3 Pressurization system

9.3.1 Room pressure differential

The pressurization system shall be capable of maintaining a pressure of at least 25 Pa in the room with all outlets open

9.3.2 Power for pressurization system

The pressurization system shall be capable of being energized independently from the electrical power to the room

9.4 Preventing the explosive atmosphere from entering an open door

Entry of an explosive atmosphere through an open door shall be prevented by an airlock in accordance with 9.5, or by a minimum outward velocity of air through the open door in accordance with 9.6

Exceptions are:

• doors marked “restricted access”, opened less than three times a day for no longer than

60 s each time, arranged to alarm at an attended location on being opened or not fully closed with an optional time delay of not more than 90 s and located in a Zone 2 hazardous area;

• doors used only for infrequent movement of equipment, if, under conditions of management control, these doors are marked to restrict use, are not used for egress, and are secured in the closed position;

• doors used only as emergency exits and that only open from the inside

9.5 Airlock

Provision shall be made to ensure that the airlock either has a continuous flow of clean air equivalent to 5 volumes of the airlock per hour, or that gas detectors are installed within the airlock arranged to alarm at 25 % of the limiting value (see gas detectors in 8.3)

NOTE 1 It is the user’s responsibility to provide prompt restorative action if the gas detectors within the airlock indicate a level in excess of 25 % of the limiting value for a period of time

Each door of the airlock shall be fitted with a device to indicate locally when the doors are not closed

NOTE 2 An additional indication at an attended location is recommended

Any electrical equipment within the airlock shall be suitable for the external area classification