SIST EN 12255-10:2023
(Main)Wastewater treatment plants - Part 10: Safety principles
Wastewater treatment plants - Part 10: Safety principles
This document defines minimum safety requirements to be observed in the planning, construction or reconstruction of wastewater treatment plants.
The purpose of this document is to ensure the protection of people.
Kläranlagen - Teil 10: Sicherheitstechnische Baugrundsätze
Dieses Dokument legt sicherheitstechnische Mindestanforderungen fest, die bei der Planung, dem Bau oder dem Umbau von Kläranlagen zu beachten sind.
Zweck dieses Dokuments ist es, den Schutz von Personen sicherzustellen.
Stations d’épuration - Partie 10 : Principes de sécurité
Le présent document définit les exigences minimales de sécurité à respecter lors de la planification, de la
construction ou de la reconstruction des stations d’épuration.
Le présent document a pour objet de garantir la protection des personnes.
Čistilne naprave za odpadno vodo - 10. del: Varnostna načela
Ta dokument določa minimalne varnostne zahteve, ki jih je treba upoštevati pri načrtovanju, gradnji in rekonstrukciji čistilnih naprav za odpadno vodo.
Namen tega dokumenta je zagotoviti zaščito ljudi.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 12255-10:2023
01-maj-2023
Nadomešča:
SIST EN 12255-10:2001
Čistilne naprave za odpadno vodo - 10. del: Varnostna načela
Wastewater treatment plants - Part 10: Safety principles
Kläranlagen - Teil 10: Sicherheitstechnische Baugrundsätze
Stations d’épuration - Partie 10 : Principes de sécurité
Ta slovenski standard je istoveten z: EN 12255-10:2023
ICS:
13.060.30 Odpadna voda Sewage water
SIST EN 12255-10:2023 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN 12255-10:2023
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SIST EN 12255-10:2023
EN 12255-10
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2023
EUROPÄISCHE NORM
ICS 13.060.30 Supersedes EN 12255-10:2000
English Version
Wastewater treatment plants - Part 10: Safety principles
Stations d'épuration - Partie 10 : Principes de sécurité Kläranlagen - Teil 10: Sicherheitstechnische
Baugrundsätze
This European Standard was approved by CEN on 6 February 2023.
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
© 2023 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 12255-10:2023 E
worldwide for CEN national Members.
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SIST EN 12255-10:2023
EN 12255-10:2023 (E)
Contents Page
European foreword . 3
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Symbols and abbreviations . 6
5 Requirements . 6
5.1 General . 6
5.2 Confined spaces . 7
5.3 Hazardous substances . 8
5.4 Warning systems for the safety of persons . 8
5.5 Open water . 8
5.6 Vehicular and pedestrian traffic routes . 9
5.6.1 Access considerations . 9
5.6.2 Operational considerations . 9
5.6.3 Passageways. 10
5.6.4 Steps and ramps. 10
5.7 Fixed ladders, manhole steps and staircases . 10
5.8 Manholes and manways . 10
5.9 Falling preventions and covers . 11
5.10 Emergency exits . 11
5.11 Work places, work platforms and maintenance platforms . 12
5.12 Lifting equipment . 12
5.13 Electrical installations . 12
5.14 Ventilation . 12
5.15 Areas at risk from explosions . 13
5.16 Hygienic facilities . 13
5.17 General warning signs . 14
6 Special requirements . 15
6.1 Systems for separating solids from wastewater . 15
6.2 Wastewater pumping stations . 15
6.3 Aeration tanks . 16
6.4 Digestion tanks, low-pressure gasholders . 16
6.5 Digester gas pipes . 16
6.6 Desulphurizing plants . 17
6.7 Gas engine rooms and gas engines . 17
6.8 Gas flares . 18
6.9 Sludge dewatering . 18
6.10 Installations for storage and handling of chemicals and hazardous substances . 18
Annex A (informative) Relevant standards containing safety requirements . 19
Annex B (informative) Relevant EC Directives that contain safety requirements . 22
Bibliography . 24
2
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SIST EN 12255-10:2023
EN 12255-10:2023 (E)
European foreword
This document (EN 12255-10:2023) has been prepared by Technical Committee CEN/TC 165 “Waste
water engineering”, the secretariat of which is held by DIN.
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 September 2023, and conflicting national standards
shall be withdrawn at the latest by September 2023.
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 12255-10:2000.
This is the tenth part prepared by Working Group CEN/TC 165/WG 40 relating to the general
requirements and processes for treatment plants for a total number of inhabitants and population
equivalents (PT) over 50.
The EN 12255 series, Wastewater treatment plants, consists of the following parts:
— Part 1: General construction principles
— Part 2: Storm management systems
— Part 3: Preliminary treatment
— Part 4: Primary treatment
— Part 5: Lagooning processes
— Part 6: Activated sludge process
— Part 7: Biological fixed-film reactors
— Part 8: Sludge treatment and storage
— Part 9: Odour control and ventilation
— Part 10: Safety principles
— Part 11: General data required
— Part 12: Control and automation
— Part 13: Chemical treatment — Treatment of wastewater by precipitation/flocculation
— Part 14: Disinfection
— Part 15: Measurement of the oxygen transfer in clean water in aeration tanks of activated sludge
plants
— Part 16: Physical (mechanical) filtration
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SIST EN 12255-10:2023
EN 12255-10:2023 (E)
NOTE Part 2 is under preparation.
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.
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SIST EN 12255-10:2023
EN 12255-10:2023 (E)
Introduction
Differences in wastewater treatment throughout Europe have led to a variety of systems being
developed. This document gives fundamental information about the systems; this document has not
attempted to specify all available systems. A generic arrangement of wastewater treatment plants is
illustrated below in Figure 1:
Key
1 preliminary treatment
2 primary treatment
3 secondary treatment
4 tertiary treatment
5 additional treatment (e.g. disinfection or removal of micropollutants)
6 sludge treatment
7 lagoons (as an alternative)
A raw wastewater
B effluent for re-use (e.g. irrigation)
C discharged effluent
D screenings and grit
E primary sludge
F secondary sludge
G tertiary sludge
H stabilized sludge
I digester gas
J returned water from dewatering
Figure 1 — Schematic diagram of wastewater treatment plants
The primary application is for wastewater treatment plants designed for the treatment of domestic and
municipal wastewater.
NOTE For requirements on pumping installations at wastewater treatment plants see EN 752, Drain and
sewer systems outside buildings and the EN 16932 series, Drain and sewer systems outside buildings — Pumping
systems:
— Part 1: General requirements;
— Part 2: Positive pressure systems;
— Part 3: Vacuum systems.
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SIST EN 12255-10:2023
EN 12255-10:2023 (E)
1 Scope
This document defines minimum safety requirements to be observed in the planning, construction or
reconstruction of wastewater treatment plants.
The purpose of this document is to ensure the protection of people.
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 476, General requirements for components used in drains and sewers
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:
— IEC Electropedia: available at https://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
3.1
confined space
space in which the ventilation is restricted to the extent that special safety precautions need to be taken
[SOURCE: EN 16323:2014, term number 2.1.3.4]
3.2
manway
tightly lockable access opening in containers, tanks, vessels, boilers, bunkers etc. through which a
person can enter to perform inspection or repair work
4 Symbols and abbreviations
ATEX Explosive Atmospheres (ATEX) Directives (2014/34/EU and 1999/92/EC)
LEL lower explosive limit
5 Requirements
5.1 General
Compliance with safety regulations is an integral part of the design and construction of the facilities.
National or local regulations can exceed the requirements laid down in this document. In those
jurisdictions that are bound by European Commission Directives, many aspects of safety have been
enshrined in law so are not repeated in this document. For places not covered by such laws these
Directives can be a useful guide for good practice. Accordingly, a list of the key Directives is given in
Annex B in addition to a list of standards that contain detailed requirements (e.g. for machinery
installations).
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SIST EN 12255-10:2023
EN 12255-10:2023 (E)
The primary consideration should be the avoidance of accidents and harmful incidents where
foreseeable. Consideration of mitigation measures should be an additional layer of protection not an
alternative.
5.2 Confined spaces
Toxic, explosive or oxygen deficient atmospheres can easily arise in confined spaces either enclosed or
sunken where gasses can collect. They can also lead to high temperatures arising (e.g. inside protective
clothing) which can make them unsuitable environments to carry out work. Typically, confined spaces
in wastewater treatment plants include:
— conduits;
— shafts, inspection manholes, seepage water shafts;
— basins (covered or sunken);
— drop structures;
— valve structures;
— inlet and outlet structures;
— sunken or enclosed screening plants;
— pumping stations (dry or wet wells);
— sludge silos and covered thickeners;
— aerobic or anaerobic digestion tanks;
— gasholders (gasometers);
— completely covered plants.
The need to enter such spaces in order to carry out maintenance or inspections shall be minimized by
design. Examples of how to achieve this include:
— ensuring equipment can be removed from the confined space in order for it to be maintained in an
area that is a safe environment;
— installation of sensors rather than inspection points.
To prevent unauthorised access (e.g. by people who might not understand the associated risks), entry
points to such confined spaces shall be adequately secured.
However, it is likely that all spaces will ultimately require access even if those occasions are rare.
Therefore, suitably secured access should be provided and provision made for any temporary or
permanent equipment that might be needed to undertake the work safely and for the potential need to
rescue personnel.
Fixed or portable gas monitoring equipment shall be employed; portable gas monitoring shall be
operable from safe places (see 5.4).
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SIST EN 12255-10:2023
EN 12255-10:2023 (E)
5.3 Hazardous substances
Hazards from substances in wastewater treatment plants can arise from solid substances, liquids,
vapours, gases and bio-aerosols, microorganisms and dust particles in a dangerous quantity or
concentration and through the presence of oxygen-displacing media.
Hazards can also arise from substances being introduced from an external source or can be produced in
situ by biological processes (e.g. fermentation, putrefaction) or by chemical reactions (e.g. when
different wastewaters are mixed).
Hazards can arise from the following sources:
— gases or vapours which can cause fires or explosions;
— oxygen deficiency which can result in suffocation;
— toxic, corrosive, irritant, flammable or hot substances, which can cause harm to health by contact,
absorption through the skin or by ingestion, inhalation, or penetration through puncture wounds;
— increase of flow or level of water, e.g. following heavy rain or flooding;
— microorganisms and their metabolic products which can result in infections;
— radioactive substances.
Where possible, designs should seek to avoid creating the circumstances leading to the formation of the
hazard. Where this is not possible designs should seek to keep the hazard separated from people.
5.4 Warning systems for the safety of persons
Fixed provision shall be made to enable monitoring the atmosphere in frequently entered confined
spaces and other areas where hazardous atmospheres are foreseeable to ensure that health risks for
persons can be avoided. Where personnel will only need to enter areas under exceptional
circumstances it may be assumed that portable monitoring systems will be used.
Fixed monitoring equipment may also be used to actuate emergency systems (e.g. switching on
ventilation). The activation of these means shall be indicated by appropriate signals.
The monitoring equipment shall be tested to ensure reliability and shall be explosion protected.
There shall be an adequate means of communication between authorized personnel on the wastewater
treatment site, e.g. telephone or radio.
5.5 Open water
Open tanks, lagoons and channels present risks of drowning.
Prevention of unauthorized or accidental access by personnel and animals should be the primary
method of avoiding dangerous incidents (e.g. people rescuing pets, livestock or other animals that have
strayed or fallen into the water). This is typically achieved by fencing or raising of tank sides to be
above ground level.
Signage warning of deep or fast flowing water is also required.
The installation of a floating device or float-and-retrieval ring near lagoons or other expanses of water,
should be considered where it is impractical to provide complete security by other means.
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SIST EN 12255-10:2023
EN 12255-10:2023 (E)
5.6 Vehicular and pedestrian traffic routes
5.6.1 Access considerations
Vehicular and pedestrian traffic routes shall be laid out to provide safe access to and egress from
operational work places and maintenance positions. They shall be free of obstacles over which persons
might trip, well-lit and shall be constructed in such a way that they can be kept safe to walk along when
wet or icy.
This requirement is adequately satisfied, if e.g.:
— work places can be reached as directly and conveniently as possible;
— paths are even and not obstructed by parts of the plant and there are no obstacles on the paths such
as pipeline crossings and they are not obstructed by the operation of valves;
— obstacles such as open channels or conveyor belts are bridged over;
— floors are easy to clean;
— floor coverings, gratings, roads and paths have non-slip surfaces, and collection of water on the
surfaces is prevented;
— paths are constructed of materials which are resistant against wear and tear;
— slabs and pavings are laid even and with narrow joints;
— non-slip surfaces allow safe walking in every direction under adverse conditions;
— doors of emergency exits open to the outside.
5.6.2 Operational considerations
Traffic routes and thoroughfares shall be laid out in such a way as to prevent risks from vehicles during
operation.
This requirement is adequately satisfied, if e.g.:
— traffic routes are kept free from installations so that they can be used at any time;
— traffic routes for vehicles where passing doors, gates, passageways, thoroughfares, or stair-exits
shall have a minimum 1,0 m clearance between the exit and the traffic way. Blind exits shall be
protected, e.g. by use of diversion barriers or mirrors;
— traffic routes are present in adequate numbers and their layout and dimensions are such that they
can be used safely by pedestrians or vehicles according to their function, e.g. adequate turning
areas for vehicles;
— traffic routes for motorized or rail-mounted means of transport are wide enough to maintain a
minimum safety distance of 0,5 m on both sides of traffic routes between the outer edge of the
means of transport and the boundary of the traffic route;
— lighting equipment on traffic routes is located and designed such that the lighting itself cannot
cause any accident hazard; and the intensity of general lighting is at least 5 lux;
— speed limits have been considered.
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SIST EN 12255-10:2023
EN 12255-10:2023 (E)
5.6.3 Passageways
Passageways shall be a minimum of 2,0 m high and 0,6 m wide. If they are used for transporting loads
they should be a minimum of 1,2 m wide.
5.6.4 Steps and ramps
Steps or ramps shall be provided for height differences of more than 0,2 m. Ramps shall not be steeper
than 1 : 10 and shall be constructed without steps. Where steps and ramps are not possible, see 5.7.
5.7 Fixed ladders, manhole steps and staircases
If steps or ramps are not possible for structural reasons, fixed ladders, step irons, staircases or other
access facilities shall be provided.
Fixed ladders, manhole steps and staircases shall be of non-slip design and shall offer adequate foot
room.
Where water, oil or grease may be present, additional means of slip prevention such as profiling or
coatings shall be used.
Fixed ladders shall have a minimum distance to the wall of 150 mm.
Where there is the danger of falling more than 3 m in height there shall be installed permanent
equipment to prevent falling (e.g. safety rails for sledge and safety belt and where appropriate, fixing
points for fall arresters).
Safety cages are not allowed around ladders in potentially confined spaces, where they may hinder the
rescue of injured persons.
Suitable access aids shall be provided above access points for climbing on and off safely.
This requirement is adequately satisfied if e.g.:
— sleeves are built into the manhole cover frames into which projecting positively fixed gripping bars
can be inserted which extend a minimum of 1,1 m above the cover frame;
— existing railings provide a handhold;
— a man-riding winch can be used.
Rest platforms shall be provided in maximum interval of 6 m on all steps or fixed ladders with a length
of more than 10 m above ground or 6 m. into confined spaces in such a way that the rescue of injured
persons and the transport of tools and materials will not be hindered.
The clearance on the user’s side of fixed ladders shall be not less than 0,65 m for vertical ladders and
not less than 1,1 m for sloping ladders.
5.8 Manholes and manways
Manhole shafts shall have a minimum width of DN/ID 1 000 (according to EN 476).
The clear width of manhole covers in vehicular traffic areas shall be not less than DN/ID 600. In non-
traffic areas manhole covers should have a minimum clear width of DN/ID 800 (according to EN 124-1).
Manways shall have a minimum diameter of 500 mm and should have a diameter between 600 mm and
1000 mm (where possible).
NOTE In the vast majority of Member States the safe clear opening is considered to be at least 600 mm
for man entry. In some other Member States larger openings are required.
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SIST EN 12255-10:2023
EN 12255-10:2023 (E)
5.9 Falling preventions and covers
Work places and traffic routes adjacent to a vertical drop or other dangerous areas shall have
permanent guardrails to prevent persons falling or entering these dangerous areas. For additional
information on the maximum allowable vertical drop height not prevented by those guardrails etc., see
national regulations.
When there is no special risk of falling into open channels or basins, tensioned chains, ropes or nets
may be used.
Suitable protection against falling is provided e.g. by 1,1 m high permanently fixed railings or enclosing
walls.
The protective barriers shall be constructed so as to prevent persons falling through.
In the case of protective barriers with vertical intermediate bars, the clear distance between the bars
shall not exceed 0,18 m. For protective barriers with one or more knee-height rails, the distance
between toe board and rail, between rail and hand-rail or between two intermediate rails shall not
exceed 0,5 m.
In the absence of toe boards, the distance between ground and knee-height rail shall not exceed 0,3 m.
Toe boards shall be a minimum of 0,1 m high and shall be installed above all working-places and traffic
routes, independent of the structure of protective barriers.
The protective barriers shall be constructed and fixed so they can withstand a horizontal force of
1 000 N/m at their upper edge. Alternatively, a design load of 500 N/m is sufficient for protective
barriers on platforms or stairways and walkways with vertical traffic loads of maximum 5 000 N/m, or
of 300 N/m for barriers in areas or on routes which are only used for control and maintenance
purposes (e.g. tank roofs, inspection apertures on furnaces) and on vehicles and for slot-in railings.
The values quoted are design load values for the static calculation of the protective barrier.
Suitable trees, bushes and hedges can provide means of fall prevention on slopes with an incline up to
1 : 1.
If removable safety barriers are required, they shall be of the hinged, slidable or slot-in type. Removable
safety barriers may be necessary, for example, at access points to ladders and stairways or at
installation access apertures.
Covers shall be protected against unintentional displacement and shall withstand the operational and
climatic stresses.
This requirement is adequately satisfied if e.g.:
— covers can be opened from safe standing positions;
— hinged covers can be secured in the open position;
— heavy covers are additionally equipped with counterbalances, hydraulically or mechanically
actuated lifting devices or pneumatic springs.
5.10 Emergency exits
Tanks shall be equipped with permanently installed emergency exits in every self-contained basin
section. One permanently installed emergency exit shall be reached within a range of 15 m to swim.
Ladders, manhole steps and staircases, reaching down a minimum of 1,0 m below the lowest
operational water level, may be used as emergency exits.
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SIST EN 12255-10:2023
EN 12255-10:2023 (E)
Open tanks with sloped walls with inclines up to 1 : 2 may be equipped with other means (e.g. durable
netting) for assisting climbing out.
5.11 Work places, work platforms and maintenance platforms
Work places, work platforms and maintenance platforms shall be arranged, set up and designed free of
obstacles and so that it is possible to work safely on them, even if wet or icy. This applies in particular
with regard to the material, their spaciousness, strength and stability, surface, non-slip qualities,
illumination and ventilation and with regard to avoiding harmful environmental effects and hazards
caused by third parties.
The requirement for non-slipperiness also includes the requirement that gratings and standing
positions shall where possible be located safe from flooding.
5.12 Lifting equipment
Suitable and sufficient lifting equipment shall be available for the handling of heavy loads.
This requirement is adequately satisfied if e.g.:
— a lifting device is installed;
— a support for a mobile hoist is built in;
— provision is made for a tripod and portable lifting hoist to be u
...
SLOVENSKI STANDARD
oSIST prEN 12255-10:2021
01-september-2021
Čistilne naprave za odpadno vodo - 10. del: Varnostna načela
Wastewater treatment plants - Part 10: Safety principles
Kläranlagen - Teil 10: Sicherheitstechnische Baugrundsätze
Stations d'épuration - Partie 10: Principes de sécurité
Ta slovenski standard je istoveten z: prEN 12255-10
ICS:
13.060.30 Odpadna voda Sewage water
oSIST prEN 12255-10:2021 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST prEN 12255-10:2021
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oSIST prEN 12255-10:2021
DRAFT
EUROPEAN STANDARD
prEN 12255-10
NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2021
ICS 13.060.30 Will supersede EN 12255-10:2000
English Version
Wastewater treatment plants - Part 10: Safety principles
Stations d'épuration - Partie 10: Principes de sécurité Kläranlagen - Teil 10: Sicherheitstechnische
Baugrundsätze
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 165.
If this draft becomes a European Standard, 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.
This draft European Standard was established by CEN 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, Turkey and
United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.
Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 12255-10:2021 E
worldwide for CEN national Members.
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oSIST prEN 12255-10:2021
prEN 12255-10:2021 (E)
Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Symbols and abbreviations . 5
5 Requirements . 5
5.1 General. 5
5.2 Confined spaces . 6
5.3 Hazardous substances . 6
5.4 Warning systems for the safety of persons . 7
5.5 Open water . 7
5.6 Vehicular and pedestrian traffic routes . 7
5.6.1 Access considerations . 7
5.6.2 Operational considerations . 8
5.6.3 Passageways . 8
5.6.4 Steps and ramps . 8
5.7 Fixed ladders, manhole steps and staircases . 9
5.8 Manholes . 9
5.9 Falling preventions and covers . 9
5.10 Emergency exits . 10
5.11 Work places, work platforms and maintenance platforms . 10
5.12 Lifting equipment . 10
5.13 Electrical installations . 11
5.14 Ventilation . 11
5.15 Areas at risk from explosions . 11
5.16 Hygienic facilities . 12
5.17 General warning signs . 12
6 Special requirements . 13
6.1 Systems for separating solids from wastewater . 13
6.2 Wastewater pumping stations . 13
6.3 Aeration tanks . 14
6.4 Digestion tanks, low-pressure gasholders. 14
6.5 Digester gas pipes . 15
6.6 Desulphurizing plants . 15
6.7 Gas engine rooms and gas engines . 15
6.8 Gas flares . 16
6.9 Sludge dewatering . 16
6.10 Installations for storage and handling of chemicals and hazardous substances . 16
Annex A (informative) Relevant standards containing safety requirements . 18
Annex B (informative) Relevant EC Directives that contain safety requirements . 21
Bibliography . 23
2
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oSIST prEN 12255-10:2021
prEN 12255-10:2021 (E)
European foreword
This document (prEN 12255-10:2021) has been prepared by Technical Committee CEN/TC 165 “Waste
water engineering”, the secretariat of which is held by DIN.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 12255-10:2000.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association, and supports essential requirements of EU Directive(s).
This is the tenth part prepared by Working Group CEN/TC 165/WG 40 relating to the general
requirements and processes for treatment plants for a total number of inhabitants and population
equivalents (PT) over 50.
The EN 12255 series with the generic title “Wastewater treatment plants” consists of the following
parts:
— Part 1: General construction principles
— Part 2: Storm management systems
— Part 3: Preliminary treatment
— Part 4: Primary settlement
— Part 5: Lagooning processes
— Part 6: Activated sludge process
— Part 7: Biological fixed-film reactors
— Part 8: Sludge treatment and storage
— Part 9: Odour control and ventilation
— Part 10: Safety principles
— Part 11: General data required
— Part 12: Control and automation
— Part 13: Chemical treatment — Treatment of wastewater by precipitation/flocculation
— Part 14: Disinfection
— Part 15: Measurement of the oxygen transfer in clean water in aeration tanks of activated sludge
plants
— Part 16: Physical (mechanical) filtration
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Introduction
Differences in wastewater treatment throughout Europe have led to a variety of systems being
developed. This document gives fundamental information about the systems; this document has not
attempted to specify all available systems. A generic arrangement of wastewater treatment plants is
illustrated below:
Key
1 preliminary treatment
2 primary treatment
3 secondary treatment
4 tertiary treatment
5 additional treatment (e.g. disinfection or removal of micropollutants)
6 sludge treatment
7 lagoons (as an alternative)
A raw wastewater
B effluent for re-use (e.g. irrigation)
C discharged effluent
D screenings and grit
E primary sludge
F secondary sludge
G tertiary sludge
H digested sludge
I digester gas
J returned water from dewatering
Figure 1 — Schematic diagram of wastewater treatment plants
The primary application is for wastewater treatment plants designed for the treatment of domestic and
municipal wastewater.
NOTE For requirements on pumping installations at wastewater treatment plants see EN 752, Drain and
sewer systems outside buildings and EN 16932, Drain and sewer systems outside buildings — Pumping systems:
— Part 1: General requirements;
— Part 2: Positive pressure systems;
— Part 3: Vacuum systems.
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1 Scope
This document defines minimum safety requirements to be observed in the planning, construction or
reconstruction of wastewater treatment plants.
The purpose of this document is to ensure the protection of people.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at https://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
3.1
confined space
space in which the ventilation is restricted to the extent that special safety precautions need to be taken
[SOURCE: EN 16323:2014, term number 2.1.3.4]
4 Symbols and abbreviations
ATEX Explosive Atmospheres (ATEX) Directives (2014/34/EU and 1999/92/EC)
LEL lower explosive limit
5 Requirements
5.1 General
Compliance with safety regulations should be an integral part of the design and construction of the
facilities. National or local regulations may exceed the requirements laid down in this standard. In this
case the requirements of those regulations should be observed. In those jurisdictions that are bound by
European Commission Directives, many aspects of safety have been enshrined in law so are not
repeated in this European standard. For places not covered by such laws these Directives can be a
useful guide for good practice. Accordingly a list of the key Directives is given in Annex B in addition to a
list of standards that contain detailed requirements (e.g. for machinery installations).
The primary consideration should be the avoidance of accidents and harmful incidents where
foreseeable. Consideration of mitigation measures should be an additional layer of protection not an
alternative.
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5.2 Confined spaces
Toxic, explosive or oxygen deficient atmospheres can easily arise in confined spaces either enclosed or
sunken where gasses can collect. They can also lead to high temperatures which can make them
unsuitable environments to carry out work. Typically confined spaces in wastewater treatment plants
include:
— conduits;
— shafts, inspection manholes, seepage water shafts;
— basins (covered or sunken);
— drop structures;
— valve structures;
— inlet and outlet structures;
— sunken or enclosed screening plants;
— pumping stations (dry or wet wells);
— sludge silos and covered thickeners;
— digestion tanks;
— gasholders (gasometers);
— completely covered plants.
The need to enter such spaces in order to carry out maintenance or inspections shall be minimized by
design. Examples of how to achieve this include:
— ensuring equipment can be extracted from the confined space in order for it to be maintained;
— installation of sensors rather than inspection points.
To prevent unauthorised access by people who may not understand the associated risks, entry points to
such confined spaces shall be adequately secured.
However it is likely that all spaces will ultimately require access even if those occasions are rare.
Therefore suitably secured access should be provided and provision made for any temporary or
permanent equipment that might be needed to undertake the work safely and for the potential need to
rescue personnel.
Fixed or portable monitoring equipment shall be employed; portable monitoring shall be operable from
places of safety (see 5.4).
5.3 Hazardous substances
Hazards from substances in wastewater treatment plants can arise from solid substances, liquids,
vapours, gases and bio-aerosols, microorganisms and dust particles in a dangerous quantity or
concentration and through the presence of oxygen-displacing media.
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Hazards can also arise from substances being introduced from an external source or can be produced in
situ by biological processes (e.g. fermentation, putrefaction) or by chemical reactions (e.g. when
different wastewaters are mixed).
Hazards can arise from the following sources:
— gases or vapours which can cause fires or explosions;
— oxygen deficiency which can result in suffocation;
— toxic, corrosive, irritant, flammable or hot substances, which can cause harm to health by contact,
absorption through the skin or by ingestion, inhalation, or penetration through puncture wounds;
— increase of flow or level of water, e.g. following heavy rain or flooding;
— microorganisms and their metabolic products which can result in infections;
— radioactive substances.
Where possible, designs should seek to avoid creating the circumstances leading to the formation of the
hazard. Where this is not possible designs should seek to keep the hazard separated from people.
5.4 Warning systems for the safety of persons
Fixed provision shall be made to enable monitoring the atmosphere in frequently entered confined
spaces and other areas where hazardous atmospheres are foreseeable to ensure that health risks for
persons can be avoided. Where personnel will only need to enter areas under exceptional
circumstances it may be assumed that portable monitoring systems will be used.
Fixed monitoring equipment may also be used to actuate emergency systems (e.g. switching on
ventilation). The activation of these means shall be indicated by appropriate signals.
The monitoring equipment shall be tested to ensure reliability and shall be explosion protected.
There shall be an adequate means of communication between authorized personnel on the wastewater
treatment site, e.g. telephone or radio.
5.5 Open water
Open tanks, lagoons and channels present risks of drowning.
Prevention of unauthorized or accidental access by personnel and animals should be the primary
method of avoiding dangerous incidents (e.g. people rescuing pets, livestock or other animals that have
strayed or fallen into the water). This is typically achieved by fencing or raising of tank sides to be
above ground level.
Signage warning of deep or fast flowing water is also required.
The installation of a floating device or float-and-retrieval ring near lagoons or other expanses of water,
should be considered where it is impractical to provide complete security by other means.
5.6 Vehicular and pedestrian traffic routes
5.6.1 Access considerations
Vehicular and pedestrian traffic routes shall be laid out to provide safe access to and egress from
operational work places and maintenance positions. They shall be free of obstacles over which persons
might trip, well-lit and shall be constructed in such a way that they can be kept safe to walk along when
wet or icy.
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This requirement is adequately satisfied, if e.g.:
— work places can be reached as directly and conveniently as possible;
— paths are even and not obstructed by parts of the plant and there are no obstacles on the paths such
as pipeline crossings and they are not obstructed by the operation of valves;
— obstacles such as open channels or conveyor belts are bridged over;
— floors are easy to clean;
— floor coverings, gratings, roads and paths have non-slip surfaces, and collection of water on the
surfaces is prevented;
— paths are constructed of materials which are resistant against wear and tear;
— slabs and pavings are laid even and with narrow joints;
— non-slip surfaces allow safe walking in every direction under adverse conditions;
— doors of emergency exits open to the outside.
5.6.2 Operational considerations
Traffic routes and thoroughfares shall be laid out in such a way as to prevent risks from vehicles during
operation.
This requirement is adequately satisfied, if e.g.:
— traffic routes are kept free from installations so that they can be used at any time;
— traffic routes for vehicles where passing doors, gates, passageways, thoroughfares, or stair-exits
shall have a minimum 1,0 m clearance between the exit and the traffic way. Blind exits shall be
protected, e.g. by use of diversion barriers or mirrors;
— traffic routes are present in adequate numbers and their layout and dimensions are such that they
can be used safely by pedestrians or vehicles according to their function, e.g. adequate turning
areas for vehicles;
— traffic routes for motorized or rail-mounted means of transport are wide enough to maintain a
minimum safety distance of 0,5 m on both sides of traffic routes between the outer edge of the
means of transport and the boundary of the traffic route;
— lighting equipment on traffic routes is located and designed such that the lighting itself cannot cause
any accident hazard; and the intensity of general lighting is at least 5 lux;
— speed limits have been considered.
5.6.3 Passageways
Passageways shall be a minimum of 2,0 m high and 0,6 m wide. If they are used for transporting loads
they should be a minimum of 1,2 m wide.
5.6.4 Steps and ramps
Steps or ramps shall be provided for height differences of more than 0,2 m. Ramps shall not be steeper
than 1 : 10 and shall be constructed without steps. Where steps and ramps are not possible see 5.7.
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5.7 Fixed ladders, manhole steps and staircases
If steps or ramps are not possible for structural reasons, fixed ladders, step irons, staircases or other
access facilities shall be provided.
Fixed ladders, manhole steps and staircases shall be of non-slip design and shall offer adequate foot
room.
Where water, oil or grease may be present, additional means of slip prevention such as profilings or
coatings shall be used.
Fixed ladders shall have a minimum distance to the wall of 150 mm.
Where there is the danger of falling more than 3 m in height there shall be installed permanent
equipment to prevent falling (e.g. safety rails for sledge and safety belt and where appropriate, fixing
points for fall arresters).
Safety cages are not allowed around ladders in potentially confined spaces, where they may hinder the
rescue of injured persons.
Suitable access aids shall be provided above access points for climbing on and off safely.
This requirement is adequately satisfied if e.g.:
— sleeves are built into the manhole cover frames into which projecting positively fixed gripping bars
can be inserted which extend a minimum of 1,1 m above the cover frame;
— existing railings provide a handhold;
— a man-riding winch can be used.
Rest platforms shall be provided in maximum interval of 6 m on all steps or fixed ladders with a length
of more than 10 m above ground or 6 m. into confined spaces in such a way that the rescue of injured
persons and the transport of tools and materials will not be hindered.
The clearance on the users side of fixed ladders shall be not less than 0,65 m for vertical ladders and not
less than 1,1 m for sloping ladders.
5.8 Manholes
Manhole shafts shall have a minimum width of DN/ID 1 000 (according to EN 476).
The clear width of manhole covers in vehicular traffic areas shall be not less than DN/ID 600. In non-
traffic areas manhole covers should have a minimum clear width of DN/ID 800 (according to EN 124.)
5.9 Falling preventions and covers
Work places and traffic routes adjacent to a vertical drop or other dangerous areas shall have
permanent guardrails to prevent persons falling or entering these dangerous areas. For the maximum
allowable vertical drop height not prevented by those guardrails etc., see national regulations.
When there is no special risk of falling into open channels or basins, tensioned chains, ropes or nets
may be used.
Suitable protection against falling is provided e.g. by a minimum of 1,0 m high permanently fixed
railings or enclosing walls.
The protective barriers shall be constructed so as to prevent persons falling through.
In the case of protective barriers with vertical intermediate bars, the clear distance between the bars
shall not exceed 0,18 m. For protective barriers with one or more knee-height rails, the distance
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between toe board and rail, between rail and hand-rail or between two intermediate rails shall not
exceed 0,5 m.
In the absence of toe boards the distance between ground and knee-height rail shall not exceed 0,3 m.
Toe boards shall be a minimum of 0,1 m high and shall be installed above all working-places and traffic
routes, independent of the structure of protective barriers.
The protective barriers shall be constructed and fixed so they can withstand a horizontal force of
1 000 N/m at their upper edge. Alternatively a design load of 500 N/m is sufficient for protective
barriers on platforms or stairways and walkways with vertical traffic loads of maximum 5 000 N/m, or
of 300 N/m for barriers in areas or on routes which are only used for control and maintenance
purposes (e.g. tank roofs, inspection apertures on furnaces) and on vehicles and for slot-in railings.
The values quoted are design load values for the static calculation of the protective barrier.
Suitable trees, bushes and hedges can provide means of fall prevention on slopes with an incline up to
1 : 1.
If removable safety barriers are required, they shall be of the hinged, slidable or slot-in type. Removable
safety barriers may be necessary, for example, at access points to ladders and stairways or at
installation access apertures.
Covers shall be protected against unintentional displacement and shall withstand the operational and
climatic stresses.
This requirement is adequately satisfied if e.g.:
— covers can be opened from safe standing positions;
— hinged covers can be secured in the open position;
— heavy covers are additionally equipped with counterbalances, hydraulically or mechanically
actuated lifting devices or pneumatic springs.
5.10 Emergency exits
Tanks shall be equipped with permanently installed emergency exits in every self-contained basin
section. One permanently installed emergency exit shall be reached within a range of 15 m to swim.
Ladders, manhole steps and staircases, reaching down a minimum of 1,0 m below the lowest
operational water level, may be used as emergency exits.
Open tanks with sloped walls with inclines up to 1 : 2 may be equipped with other means (e.g. durable
netting) for assisting climbing out.
5.11 Work places, work platforms and maintenance platforms
Work places, work platforms and maintenance platforms shall be arranged, set up and designed free of
obstacles and so that it is possible to work safely on them, even if wet or icy. This applies in particular
with regard to the material, their spaciousness, strength and stability, surface, non-slip qualities,
illumination and ventilation and with regard to avoiding harmful environmental effects and hazards
caused by third parties.
The requirement for non-slipperiness also includes the requirement that gratings and standing
positions shall where possible be located safe from flooding.
5.12 Lifting equipment
Suitable and sufficient lifting equipment shall be available for the handling of heavy loads.
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This requirement is adequately satisfied if e.g.:
— a lifting device is installed;
— a support for a mobile hoist is built in;
— provision is made for a tripod and portable lifting hoist to be used with safety devices to prevent the
legs shifting or splaying out;
— an adequate standing area is available, designed in size and in load-bearing capacity for a vehicle
with pivoted and telescopic jib (crane boom);
— safe use is possible of multi-purpose lifting appliances, e.g. equivalently equipped lorry-mounted
lifting devices, forklift trucks, small hydraulic excavators, etc.;
— lifting devices shall be certificated.
5.13 Electrical installations
Electrical equipment, its design and installation shall comply with the relevant European standards. A
list of the principal standards on this topic is given in Annex A. National and local regulations may also
apply.
5.14 Ventilation
Spaces in wastewater treatment plants, in which dangerous substances, explosive atmosphere or
aerosols can accumulate in concentrations that could be harmful to the health or in which an oxygen
deficiency can arise, shall have effective ventilation.
It shall be possible to measure the efficiency of the ventilation by testing the air quality from a safe
position.
Natural ventilation can be effective, if e.g. the design of the opening provides sufficient ventilation
without dead zones and the ventilation openings cannot be shut.
Ventilation openings which are located only at the top or bottom of a door and windows shall not be
deemed an effective means of ventilation.
Forced ventilation shall be provided if natural ventilation is not sufficient in a workspace or where
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