SIST EN 1278:2026

• Abstract:

  This document is applicable to ozone used for treatment of water intended for human consumption. It describes the characteristics of ozone, specifies tests methods for determining the ozone concentration in gases and determines rules for safe handling of the chemical ozone.

• Status: Published
• Public Enquiry End Date: 30-Jul-2024
• Publication Date: 29-Sep-2026
• ICS: 13.060.20 - Drinking water
• ICS: 71.100.80 - Chemicals for purification of water
• Technical Committee: IOVO - Water supply and waste water engineering
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 29-Sep-2026
• Due Date: 04-Dec-2026
• Completion Date: 30-Sep-2026
• Ref Project: EN 1278:2026 - Chemicals used for treatment of water intended for human consumption - Ozone

• Referred By: SIST EN 17971:2024 - Devices for in-situ generation of biocides - Ozone
• Effective Date: 17-Sep-2026
• Referred By: SIST EN 15074:2006 - Chemicals used for treatment of swimming pool water - Ozone
• Effective Date: 17-Sep-2026
• Revised: SIST EN 1278:2011 - Chemicals used for treatment of water intended for human consumption - Ozone
• Effective Date: 18-Jan-2023

SIST EN 1278:2026 is the Slovenian standard identical to EN 1278:2026 for ozone used in the treatment of water intended for human consumption. It describes the characteristics of ozone, gives methods for measuring ozone concentration in gases, and sets rules for safe handling of this chemical in drinking-water treatment. It is written for people who generate, dose, measure, specify, or supervise ozone at or near the point of use.

What does SIST EN 1278:2026 specify?

SIST EN 1278:2026 applies to ozone used for treatment of water intended for human consumption. The standard focuses on the ozone itself, while device-related matters are directed to EN 17971.

The document is organized into scope, normative references, terms and definitions, description, purity criteria, test methods, and labelling-transport-storage. It also includes one informative annex and one normative annex.

Annex	What it covers
Annex A	General information on ozone, including feed gas, uses, treatment dose, application methods, secondary effects, and operational control methods
Annex B	General rules relating to safety, including safe handling, emergency procedures, PPE, and operational safety points

What are the key requirements of SIST EN 1278:2026?

SIST EN 1278:2026 treats ozone as an unstable chemical that is generated in situ, close to where it is used. Clause 4 identifies ozone as a bluish gas with the chemical formula O3, and it notes that commercial supply is not by storage but by ozone generation devices. In practice, this means users need to specify the generator and the way ozone is produced, not a delivered bulk chemical.

Clause 5 links product purity to the feed gas and to the generation technology. The standard states that the purity requirements of EN 17971 apply, and it points out that the nominal ozone concentration at the generator operating condition shall be stated in the manufacturer’s documents. For users, this is the key specification point when selecting equipment or checking process capability.

Clause 5 also addresses impurities and by-products. Nitrogen oxides can form during generation from air, and hydrocarbons are relevant when oxygen is used as feed gas. That matters because the quality of the feed gas and the generator setup affect both performance and the chemical quality of the ozone stream.

Clause 6 points to titration and UV-absorption methods for measuring ozone concentration in gas. The detailed methods are in EN 17971. In practice, this means concentration checks are not left vague - the standard tells you where the recognized measurement methods are defined.

Clause 7 sets out the safety classification and handling framework. Ozone is assigned a hazardous classification with the signal word “Danger”, and Annex B gives the safety rules for use, emergency action, and PPE. For operators, this is the section that drives alarm settings, ventilation, and protective equipment.

Clause 7 also states that transport and storage do not apply because ozone is generated in situ and is unstable. Marking for storage is therefore not required. That is important for procurement and logistics because ozone is not handled as a storable commodity.

Annex A gives practical use information: ozone can be used for disinfection, color removal, iron and manganese removal, advanced oxidation, and coagulation assistance. It also gives guidance on dosing, residual ozone removal, and operational control methods in gas and water.

What terms does SIST EN 1278:2026 define?

• Normal temperature and pressure (NTP) - Gas conditions at 0 °C and 101 325 Pa.
• Feed gas - The gas supplied to the ozone generation device to make ozone.
• Biocidal Products Regulation (BPR) - The EU framework cited for disinfection uses of in-situ generated ozone.
• REACH - The EU chemicals regulation cited for non-biocidal uses such as oxidation.
• Oxidation-reduction potential (ORP) - A measurement used in Annex A for ozone control in water.
• Personal protection equipment (PPE) - The protective gear Annex B recommends when exposure is possible.
• Threshold limit value (TLV) - The airborne exposure limit quoted for ozone in Annex B.

Who uses SIST EN 1278:2026?

This standard is used by drinking-water treatment operators, ozone system manufacturers, water utility engineers, quality managers, laboratory staff, and safety personnel. They use it to specify ozone generation, verify ozone concentration, set operating controls, and write safe-handling procedures for in-situ ozone systems.

What changed in SIST EN 1278:2026 from the previous edition?

SIST EN 1278:2026 supersedes EN 1278:2010. The foreword lists these technical changes:

• proposed harmonized classification of ozone according to EU CLP is added;
• references for ozone use are added to EU BPR and EU REACH;
• a new threshold limit for ozone in air is included;
• EN 17971 is now referenced for ozone generation devices, and device-related matters such as installation-room safety are shifted there.

Which standards are used with SIST EN 1278:2026?

• EN 17971, Devices for in-situ generation of biocides - Ozone - This is the main companion standard. It covers device-related matters, feed gas purity, by-products, test methods, materials in contact with ozone, and operational safety topics.

What does the SIST EN 1278:2026 document contain?

The document gives identification data and physical and chemical properties for ozone, including its behavior in gas and liquid phases. It includes purity criteria, safety classification, and practical notes on decomposition, stability, and by-products. The annexes add operational guidance for water treatment use, control methods for ozone and related by-products, and emergency safety rules. It also contains tables for solubility and vapour pressure, plus a classification figure for ozone.

SLOVENSKI STANDARD
01-november-2026
Kemikalije, ki se uporabljajo za pripravo pitne vode - Ozon
Chemicals used for treatment of water intended for human consumption - Ozone
Produkte zur Aufbereitung von Wasser für den menschlichen Gebrauch - Ozon
Produits chimiques utilisés pour le traitement de l'eau destinée à la consommation
humaine - Ozone
Ta slovenski standard je istoveten z: EN 1278:2026
ICS:
13.060.20 Pitna voda Drinking water
71.100.80 Kemikalije za čiščenje vode Chemicals for purification of
water
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 1278
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2026
EUROPÄISCHE NORM
ICS 71.100.80 Supersedes EN 1278:2010
English Version
Chemicals used for treatment of water intended for human
consumption - Ozone
Produits chimiques utilisés pour le traitement de l'eau Produkte zur Aufbereitung von Wasser für den
destinée à la consommation humaine - Ozone menschlichen Gebrauch - Ozon
This European Standard was approved by CEN on 26 July 2026.

CEN 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 CEN-CENELEC Management Centre or to any CEN
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 CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

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
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 1278:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Description . 5
4.1 Identification . 5
4.2 Commercial form . 6
4.3 Physical properties . 6
4.4 Chemical properties . 8
5 Purity criteria . 8
5.1 General. 8
5.2 Composition of in-situ generated ozone gas . 8
5.3 Impurities and main by-products . 9
5.4 Chemical parameters. 9
6 Test methods . 9
7 Labelling – Transportation – Storage . 9
7.1 Materials in contact with ozone . 9
7.2 Risk and safety classification . 9
7.3 Transportation regulations and labelling . 10
7.4 Marking . 11
7.5 Stability . 11
Annex A (informative) General information on ozone . 12
A.1 Feed gas . 12
A.2 Use . 12
A.3 Operational control methods . 13
Annex B (normative) General rules relating to safety . 16
B.1 Rules for safe handling and use . 16
B.2 Emergency procedures . 16
Bibliography . 18
European foreword
This document (EN 1278:2026) has been prepared by Technical Committee CEN/TC 164 “Water supply”,
the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by March 2027, and conflicting national standards shall be
withdrawn at the latest by March 2027.
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 EN 1278:2010.
— proposed harmonized classification of ozone according to EU CLP regulation is added;
— reference for use of ozone is made to EU BPR and EU REACH regulation;
— new threshold limit for ozone in air;
— reference is made to EN 17971, standard for ozone generation devices. Device related matters are
shifted to EN 17971, e.g. operational safety of the installation room. Matters of the chemical ozone
itself remain within this document.
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.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: 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 the United
Kingdom.
Introduction
In respect of potential adverse effects on the quality of water intended for human consumption, caused
by the product covered by this document, it provides no information as to whether the product may be
used without restriction in any of the Member States of the EU or EFTA.
NOTE 1 While awaiting the adoption of verifiable European criteria, attention is drawn to national regulations.
Ozone is a biocidal product according to the Regulation (EU) No 528/2012 [1]. The use of in-situ
generated ozone for disinfection purposes falls under the provisions of the BPR, requiring access by the
user to a data set for the product authorization of ozone under the BPR. This access may be achieved
directly or indirectly e.g. via the manufacturers’ authorization for ozone generated by their devices.
Users of in-situ generated ozone should verify with their device manufacturer, if they can use ozone in
accordance with his product authorization for the disinfection of water intended for human consumption
(approved [2] under the BPR for drinking water use).
Non-biocidal use of ozone, e.g. for oxidative purposes, falls under the provisions of the REACH Regulation
[3]. The use of ozone for non-biocidal purposes requires individual access by the user to the data set
provided for the authorization of ozone under REACH.
NOTE 2 Conformity with the standard does not confer or imply authorization of the product in any of the
Member States of the EU or EFTA. The use of the product covered by this document is subject to regulation or control
by National Authorities.
1 Scope
This document is applicable to ozone used for treatment of water intended for human consumption. It
describes the characteristics of ozone, specifies tests methods for determining the ozone concentration
in gases and determines rules for safe handling of the chemical ozone.
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 17971, Devices for in-situ generation of biocides — Ozone
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp/
— IEC Electropedia: available at https://www.electropedia.org/
3.1
normal temperature and pressure of gas
NTP
gas under the conditions of normal temperature t = 0 °C and normal pressure p = 101 325 Pa
n n
3.2
feed gas
substance that is fed as gas to the ozone generation device to generate ozone
4 Description
4.1 Identification
4.1.1 Chemical name
Ozone.
General information on ozone is described in Annex A.
4.1.2 Synonym or common name
None (has sometimes been called improperly “allotropic oxygen”).
4.1.3 Relative molecular mass
48.
4.1.4 Empirical formula
O .
4.1.5 Chemical formula
O .
1)
4.1.6 CAS Registry Number
10028-15-6.
)
4.1.7 EINECS reference
Not applicable.
4.2 Commercial form
Ozone is very unstable; it is exclusively generated in-situ nearby its use by ozone generation devices.
4.3 Physical properties
4.3.1 Appearance
Bluish gas, the liquid is dark blue.
NOTE A weak absorption in the visual range between 435 nm and 475 nm.
4.3.2 Density
Gas: 2,144 kg/m at NTP (Normal Temperature Pressure, 273 K and 1 013,25 hPa = 101 325 Pa);
Liquid: 1,574 g/cm at –183 °C;
Solid: 1,728 g/cm .
4.3.3 Solubility in water
In pure water, the solubility values (S) expressed in grams per cubic meter water per (grams per cubic
meter) gas at 1 013,25 hPa are given in Table 1.
Table 1 — Solubility in water
Temperature Solubility
of water
g / m HO
°C
S, in
g / m gas
0 0,64
5 0,5
10 0,39
15 0,31
20 0,24
25 0,19
30 0,15
35 0,12
NOTE 1 Recent surveys of literature data are given in Bibliography. See [4], [5] and [6].

1)
Chemical Abstracts Service Registry Number applicable under REACH. The CAS no. is not applicable for ozone
used as a biocidal product.
2)
European Inventory of Existing Commercial Chemical Substances
NOTE 2 S is a ratio, not an absolute concentration.
4.3.4 Vapour pressure
The vapour pressure of ozone depending on temperature is given in Table 2.
Table 2 — Vapour pressure
Temperature Vapour pressure
°C hPa
−183 0,147
−180 0,28
−170 1,88
−160 8,97
−150 33,06
−140 98,92
−130 253,31
−120 569,28
−110 1 153,22
−100 21 390,79
)
4.3.5 Boiling point at 1 000 hPa
−112 °C.
NOTE Vaporization heat: 681 kJ/m at NTP.
4.3.6 Melting point
−196 °C.
4.3.7 Specific heat (liquid)
Not applicable.
4.3.8 Viscosity (dynamic)
0,004 2 Pa · s at –195 °C;
0,001 55 Pa · s at –183 °C.
4.3.9 Critical temperature
−12,1 °C.
4.3.10 Critical pressure
54 600 hPa.
3)
1000 hPa = 1 bar
4.3.11 Physical hardness
Not applicable.
4.4 Chemical properties
Ozone is a powerful oxidant and disinfectant. The standard redox potentials (ORP) at 25 °C are:
H
( E values in volts):
O
H
+ -
O + H O
O + 2H + 2e → E = 2,07 V (1)
2 2
O
H
- -
O + H O + 2e → O + 2OH E = 1,24 V (2)
3 2 2 O
H
● + - H O
E = 2,42 V (calculated value) (3)
OH + H + e → 2
O
H
If the pH increases by one unit, the E -values shall decrease by 30 mV per electron transferred. At
H
1000 hPa and 25 °C and pH = 7 the E -values, versus the normal hydrogen electrode, become:
O (1) = 1,66 V;
O (2) = 0,82 V;
●
OH (3) = 2,21V.
In water treatment most of the direct reactions of ozone are dipolar cyclo-additions and electrophilic
●
substitution reactions. Moreover ozone, in water, can generate radicals such as OH in particular at
● ●
+ H O → 2 OH + O ). The OH radical is a strong general oxidant.
alkaline pH: (O
3 2 2
5 Purity criteria
5.1 General
The purity of the generated ozone depends strongly on the purity of the feed gas and the technology of
the applied ozone generation device. The generation of ozone used for the treatment of water intended
for human consumption takes place usually by the technology of dielectric barrier discharge. This
technology uses ambient air or oxygen as feed gas for the ozone generation device to generate ozone. The
generation technology, purity requirements for the feed gas, by-products of the ozone generation, and by
products of ozone dosed in water are described in EN 17971. The purity requirements of EN 17971 apply
for this document.
NOTE Attention is drawn to national regulation for the users of ozone in order to clarify whether it is of
appropriate purity for treatment of water intended for human consumption, taking into account raw water quality,
required dosage, contents of other impurities and additives used in the product not stated in this product document.
5.2 Composition of in-situ generated ozone gas
According to EN 17971 the nominal ozone concentration using:
3 3
— clean dry air is typically 20 g ozone per m of process gas = ca. 1,5 % w/w (in practice 70 g/m = ca.
n n
5,3 % w/w can be achieved).
— oxygen as a feed gas is typically 100 g per m of process gas = ca. 7 % w/w (in practice
n
300 g/m = ca. 21 % w/w can be achieved).
n
The concentration (in grams per cubic metre NTP) at the nominal operating condition of the generators
shall be specified in the manufacturer’s documents.
5.3 Impurities and main by-products
Traces of nitrogen oxides can be formed during ozone generation forming nitrate in water, see A.3.3.
When ozone is generated from oxygen, the purity requirements of EN 17971 for hydrocarbons shall be
met, see A.3.4.
5.4 Chemical parameters
None of the substances being chemical parameters according to the Drinking Water Directive [7] are
found in the gaseous ozone phase. Pesticides and polycyclic aromatic hydrocarbons are not by-products
of the ozone manufacturing processes.
6 Test methods
The test methods by titration and by UV-absorption are described in detail in EN 17971.
...