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SLOVENSKI STANDARD
01-januar-2023
Nadomešča:
SIST-TP CEN/TR 15281:2006
Potencialno eksplozivna atmosfera - Preprečevanje eksplozij in zaščita - Vodilo o
inertizaciji za preprečitev eksplozij
Potentially explosive atmospheres - Explosion prevention and protection - Guidance on
inerting for the prevention of explosions
Atmosphères explosibles - Prévention des explosions et protection contre celles ci -
Guide de l’inertage pour la prévention des explosions
Ta slovenski standard je istoveten z: CEN/TR 15281:2022
ICS:
13.230 Varstvo pred eksplozijo Explosion protection
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
CEN/TR 15281
TECHNICAL REPORT
RAPPORT TECHNIQUE
October 2022
TECHNISCHER REPORT
ICS 13.230 Supersedes CEN/TR 15281:2006
English Version
Potentially explosive atmospheres - Explosion prevention
and protection - Guidance on inerting for the prevention of
explosions
Atmosphères explosibles - Prévention des explosions
et protection contre celles ci - Guide de l'inertage pour
la prévention des explosions
This Technical Report was approved by CEN on 9 October 2022. It has been drawn up by the Technical Committee CEN/TC 305.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 15281:2022 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 4
4 Inerting process and methods . 6
4.1 General . 6
4.2 Inerting system design and operation . 6
4.3 Establishing inert atmosphere . 8
4.4 Advanced preventive inerting (Blend inerting). 19
Annex A (informative) Formulae for pressure/vacuum-swing inerting . 38
Annex B (informative) Calculations for flow-through inerting . 41
Annex C (informative) Displacement inerting for low pressure storage tanks . 43
Annex D (informative) Prevention of diffusion of air down vent pipes . 48
Annex E (informative) Sensor technology . 50
Annex F (informative) Advanced preventive inerting method for pulverized coal grinding,
handling and storage facilities . 57
Annex G (informative) Advanced preventive inerting method applied to biomass handling and
storage facilities . 59
Bibliography . 62
European foreword
This document (CEN/TR 15281:2022) has been prepared by Technical Committee CEN/TC 305
“Potentially explosive atmospheres – Explosion prevention and protection”, the secretariat of which is
held by DIN.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes CEN/TR 15281:2006.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
1 Scope
Inerting is a preventive measure to avoid explosions or fire to happen. By feeding inert gas into a system,
which is to be protected against an explosion or a fire, the oxygen content is reduced below a certain limit
or completely replaced by an inert gas, depending on the inert gas, on the fuel and the process until no
explosion or fire can occur or develop.
Inerting can be used to prevent fire and explosion by reducing the O content.
NOTE Inerting can also be used to prevent and to extinguish smouldering nests and glowing fires which are a
primary source of ignition in pulverized fuel storage and handling facilities, substituting air by sufficient inert gas
inside the equipment.
The following cases are not covered by the guideline:
— admixture of an inert solid powder to a combustible dust;
— inerting of flammable atmospheres by wire mesh flame traps in open spaces of vessels and tanks;
— firefighting;
— avoiding an explosive atmosphere by exceeding the upper explosion limit of a flammable substance;
— anything related to product quality (oxidation or ingress of humidity) or product losses;
— any explosive atmosphere caused by other oxidizing agents than oxygen.
Other technologies might be used in combination with inerting such as floating screens made of
independent collaborative floaters consisting of an array of small floaters non-mechanically linked but
overlapping each other in order to form a continuous layer covering the liquid surface.
Product oxidation or evaporation reduction is directly proportional to the surface area covering ratio and
quality of the inerting.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
EN 13237:2012, Potentially explosive atmospheres - Terms and definitions for equipment and protective
systems intended for use in potentially explosive atmospheres
EN ISO 28300:2008, Petroleum, petrochemical and natural gas industries - Venting of atmospheric and low-
pressure storage tanks (ISO 28300:2008)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 13237:2012 and the following
apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at
— ISO Online browsing platform: available at
3.1
limiting oxygen concentration
LOC
maximum oxygen concentration in a mixture of a flammable substance and air and an inert gas, in which
an explosion will not occur, determined under specified test conditions
3.2
maximum allowable oxygen concentration
MAOC
maximum oxygen concentration in a mixture of a combustible substance and air and an inert gas, in which
an explosion will not occur, determined under specified test conditions
3.3
trip point
TP
defined value at which the process controller initiates a shut-down trip
3.4
set point
ST
defined value at which the process controller maintains the gas concentration
3.5
lower explosion limit
LEL
concentration of flammable gas or vapour in air, below which the mixture is not explosible
3.6
upper explosion limit
UEL
concentration of flammable gas or vapour in air above which the gas atmosphere is not explosible
3.7
inert gas
non-combustible gas which will not support combustion and does not react at all that avoid explosion to
occur mainly by reducing the oxygen-concentration in the protected space
Note 1 to entry: Inert can be argon, nitrogen, carbon dioxide or mixtures of these gases.
3.8
blanketing
replacement of air by an inert gas in an equipment in order to achieve inert conditions
3.9
blanketing regulator
pressure regulators used to introduce inert gas in an equipment to be inerted
3.10
breathing valve
pressure/vacuum valve
device to relieve the pressure or vacuum formed inside the cargo tanks by opening the valves at the
designated setting value to protect the tank from over-pressure or vacuum exceeding the design
parameters of the tanks
3.11
flame arrester
device fitted to the opening of an enclosure, or to the connecting pipe work of a system of enclosures, and
whose intended function is to allow flow but prevent the transmission of flame
3.12
back pressure regulator
device used to control/maintain gas pressure immediately upstream of its installed position
Note 1 to entry: It has the ability to maintain a near constant inlet pressure within design parameters, regardless
of pressure or flow fluctuations in other parts of the system.
3.13
smouldering nets
exothermic oxidation, without flaming, that is self-propagating, i.e. independent of the ignition source
Note 1 to entry: It might or might not be accompanied by incandescence.
3.14
Programmable Logic Control
PLC
electronic device designed for control of the logical sequence of events
4 Inerting process and methods
4.1 General
Many processes are routinely inerted to avoid the presence of explosive atmosphere by reducing O
content, when potential ignition sources can occur or become active. Inerting should not replace but
complement the control of ignition sources to reduce risk to an acceptable level.
Inerting requires design, procedure, maintenance and control to achieve its objective of reducing the risk
of explosive atmospheres and hence potential fires and explosions. Inerting may also introduce additional
risk to personnel through the creation of asphyxiating atmospheres in case of leakage of inerting gas in
the atmosphere, and further more environmental hazards due to entrained gases and dusts in exhausted
gas. Such risks should be taken into consideration during engineering and design phase of inerting
systems.
,
Inerting systems are a preventive measure and differ from firefighting systems (e.g. using liquid CO2
gaseous N or Argon or a dedicated mixture of gases to extinguish a fire) and curative explosion
protection systems (like suppression systems, explosion vents, etc.) that are used to minimize and reduce
the consequences or severity of a fire or an explosion that already happened.
4.2 Inerting system design and operation
4.2.1 General
To achieve adequate levels of risk reduction from an inerting system, certain design and appropriate
maintenance procedures should be followed depending on the selected technology described below.
When designing or increasing the automation of a plant or process, it is important to define safe operating
conditions. It is recommended to estimate safety levels.
Figure 1 — Oxygen concentrations to be observed when inerting equipment
Effectiveness of inert gas used decreases usually in the following order:
1) CO ;
2) Steam;
3) Flue gases;
4) N ;
5) Noble gases.
4.2.2 Design Features
a) The oxygen content of the inert gas supply (LOC is a function of the type of inert gas used and the
type of combustible used) and the target oxygen at the end of a purging process should be known
(for pressure/vacuum swing).
b) A suitable method for inerting should be chosen, and parameters selected (O analysis).
c) Calculation notes should be provided or the system should be commissioned to show it can reach
theoretical design.
4.2.3 Operational Features
a) Inert atmosphere is established as per design and before processing or handling of materials start.
b) System is maintained to keep oxygen levels within design parameters and safety parameters.
c) Cause of system failure should be defined and/or detected and corrective, or protective, actions
taken.
d) Personnel are protected, informed and trained on the potential risk of asphyxia, including for
operations planned after processing where the inerted system can be made safe for entry.
4.2.4 Information on inert gas to be taken into consideration
a) LOC depends on inert gas used thus variability of gas on an industrial site should be taken into
consideration.
b) Oxygen content of the inert gas itself can vary from few ppm to several percent, depending of the
source of supply.
c) For some onsite inert gas production methods, the oxygen concentration may vary with the rate of
production. This should be taken into consideration in the inerting procedures.
d) Availability of inert gas supply and emergency capacity with appropriate procedures in case of
supply failure.
e) Indu
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