EN 12255-1:2024

SLOVENSKI STANDARD
01-februar-2025
Čistilne naprave za odpadno vodo - 1. del: Splošna načela gradnje
Wastewater treatment plants - Part 1: General construction principles
Kläranlagen - Teil 1: Allgemeine Baugrundsätze
Stations d’épuration - Partie 1 : Principes généraux de conception et de construction
Ta slovenski standard je istoveten z: EN 12255-1:2024
ICS:
13.060.30 Odpadna voda Sewage water
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 12255-1
EUROPEAN STANDARD
NORME EUROPÉENNE
November 2024
EUROPÄISCHE NORM
ICS 13.060.30 Supersedes EN 12255-1:2002
English Version
Wastewater treatment plants - Part 1: General design and
construction principles
Stations d'épuration - Partie 1 : Principes généraux de Kläranlagen - Teil 1: Allgemeine Baugrundsätze
conception et de construction
This European Standard was approved by CEN on 27 October 2024.

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
© 2024 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 12255-1:2024 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
Introduction . 6
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 9
4 Abbreviated terms . 11
5 Requirements . 12
5.1 General requirements . 12
5.2 Design requirements . 13
5.2.1 Resilience . 13
5.2.2 Safety and accessibility . 14
5.2.3 Other design requirements . 15
5.3 Modularity . 16
5.4 Structural requirements . 16
5.4.1 General. 16
5.4.2 Dimensional tolerances . 17
5.4.3 Concrete tracks for travelling mechanical equipment (e.g. Scraper Bridges) . 17
5.4.4 Fixings and connections between equipment and structures . 17
5.4.5 Safe access . 17
5.4.6 Building ventilation . 18
5.4.7 Water supply and drainage . 18
5.4.8 Lifting equipment . 18
5.4.9 Storage and conveyance of hazardous chemicals and fuels . 18
5.5 Requirements for equipment . 19
5.5.1 Principles for mechanical design . 19
5.5.2 General design requirements . 20
5.5.3 Environmental impact . 23
5.5.4 Safety . 24
5.5.5 Documentation . 24
5.5.6 Spare parts, special tools . 24
6 Test methods . 25
6.1 Function and performance . 25
6.2 Tightness testing of concrete structures . 25
6.3 Tightness testing of other structures and equipment . 25
7 Cost Comparison Analysis . 25
Annex A (informative) Design Service Life . 26
Annex B (normative) Structural tolerances . 27
B.1 Circular tank . 27
B.1.1 Circular clarifiers with scrapers . 27
B.1.2 Circular tank with a scraper bridge travelling on the side wall (track) . 27
B.1.3 Rectangular clarifiers with scrapers . 27
Annex C (normative) Wall tracks . 28
C.1 Tracks . 28
C.2 Walls . 28
C.3 Wheels . 28
C.4 Freezing conditions . 28
Annex D (normative) Scraper Design . 29
D.1 Physical loads . 29
D.2 Driver control . 29
D.3 Bar and chain scrapers . 29
D.4 Monitoring. 30
D.5 Maintainability . 30
D.6 Design life . 30
Bibliography . 31

European foreword
This document (EN 12255-1:2024) 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 May 2025, and conflicting national standards shall be
withdrawn at the latest by May 2025.
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 12255-1:2002.
The main changes compared to the previous edition are listed below:
a) update of title and scope to incorporate design;
b) comprehensive revision and additions in all sections;
c) adaptation to the current state of the art;
d) updating of the Normative references;
e) editorial revision.
This is the first 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 design and 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 2 is under preparation.
— 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
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
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 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 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 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.
1 Scope
This document specifies the basic design and construction requirements for wastewater treatment plants
for over 50 PT.
NOTE 1 Requirements for structures which are not specific for wastewater treatment plants are not within the
scope of this document. Other ENs can apply.
NOTE 2 Equipment which is not solely used in wastewater treatment plants is subject to the applicable product
standards. However, specific requirements for such equipment when used in wastewater treatment plants are
included in this part.
NOTE 3 Although this document specifies the basic design and construction requirements for wastewater
treatment plants for over 50 PT, many requirements are only technically and economically feasible at significantly
larger sizes.
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 809, Pumps and pump units for liquids — Common safety requirements
EN 10088-2, Stainless steels — Part 2: Technical delivery conditions for sheet/plate and strip of corrosion
resisting steels for general purposes
EN 12255-9, Wastewater treatment plants — Part 9: Odour control and ventilation
EN 12255-10, Wastewater treatment plants — Part 10: Safety principles
EN 12255-13, Wastewater treatment plants — Part 13: Chemical treatment - Treatment of wastewater by
precipitation/flocculation
EN 16323, Glossary of wastewater engineering terms
EN 16932 (all parts), Drain and sewer systems outside buildings — Pumping systems
EN 60529, Degrees of protection provided by enclosures (IP Code) (IEC 60529)
EN 60034-1, Rotating electrical machines — Part 1: Rating and performance (IEC 60034-1)
EN ISO 3506-1, Fasteners — Mechanical properties of corrosion-resistant stainless steel fasteners — Part
1: Bolts, screws and studs with specified grades and property classes (ISO 3506-1)
EN ISO 3506-2, Fasteners — Mechanical properties of corrosion-resistant stainless steel fasteners — Part
2: Nuts with specified grades and property classes (ISO 3506-2)
EN ISO 14122-2:2016, Safety of machinery — Permanent means of access to machinery — Part 2: Working
platforms and walkways (ISO 14122-2:2016)
ISO 4200, Plain end steel tubes, welded and seamless — General tables of dimensions and masses per unit
length
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 16323 and the following 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
structure
construction intended to fulfil a function
[SOURCE: EN 16323:2014, definition 2.1.6.11]
3.2
equipment
component which is installed in, mounted on, attached to, or operated on structures, in the performance
of their intended function
3.3
unit
structure including any related equipment which is used as a process stage and which can be isolated
from other parallel, upstream or downstream structures
EXAMPLE A grit chamber, a clarifier, an aeration tank, a thickener, a digester.
3.4
assembly
mechanical equipment that can be removed and replaced as a whole
EXAMPLE A pump, a compressor, a gas engine, an aerator.
3.5
wastewater treatment plant
facility for the physical, biological and/or chemical treatment of wastewater
[SOURCE: EN 16323:2014, definition 2.3.9.18]
3.6
track
part of a structure on which wheels run
3.7
design mechanical load
Y
N
effective average load in continuous operation under full loading
Note 1 to entry: It is greater than or equal to the value of the operating loading which, for example, fluctuates as a
function of the given load.
3.8
continuous load bearing capacity
Y
C
load bearing capacity in continuous operation under full load
3.9
maximum loading
Y
max
peak loading which is taken as the switch-off value
Note 1 to entry: E.g. value to which overload circuit breakers are adjusted.
3.10
maximum load bearing capacity
Y
B
highest possible load bearing capacity limited to short-term load peaks, such as occur on switching on
and off
Note 1 to entry: In addition, alarm loadings YS, lying between the design loading YN and the switch-off loading Ymax,
can be agreed as required, Y and Y being stated by the equipment supplier.
N max
3.11
utilisation factor
K
A
parameter for the effects on drive units etc., intrinsic to their operation
Note 1 to entry: Usually KA includes, either directly or indirectly, information on the loading, running time and
temperature and is an overall value of the relationship between load bearing capacity and loading.
3.12
design service life
operating time until break-down of a machinery element stressed due to wear under design mechanical
load which is reached by a certain percentage of the elements tested
Note 1 to entry: As an example, the percentage for rolling bearings is 90 %.
Note 2 to entry: The design service life is different from both the warranty time and an average service life of use,
as used for cost efficiency calculations.
Note 3 to entry: The design service life is different from the cyclic design life (see 3.19).
3.13
design working life
assumed period for which a structure or part of it is to be used for its intended purpose with anticipated
repair and maintenance but without renovation or replacement being necessary
Note 1 to entry: Design working life can often be significantly longer than “design life” and is of critical importance
when calculating the longer-term resilience of drainage infrastructure, to, for example, climate change impacts.
[SOURCE: EN 1990:2023, modified to provide consistency with the terminology in EN 16323:2014]
3.14
expected service life
anticipated usage time of the plant, unit or equipment
Note 1 to entry: The horizon of cost calculations shall be based on the expected service life. It shall include
investment and repeated investment and operational costs during the design service life. Such calculations shall
include expected price increases as well as expected interest rates. Such cost calculations can be compared as
current worth values or annuities.
3.15
design horizon
length of time (or a date) in the future for which the use of the facility can be reasonably anticipated to
be required
Note 1 to entry: The design Horizon is usually equal to (or a multiple of) the Design Working Life. E.g. a design
Horizon of 60 years may be chosen for assets made up of predominantly civil structures
3.16
mode of operation
condition or manner in which a unit can operate or function
Note 1 to entry: Examples of condition include. frequency of starts, temperatures, etc.
3.17
degree of protection
protection provided by enclosures for electrical equipment against solid foreign objects, against water
and against access to hazardous parts as set out in EN 60529.
Note 1 to entry: This document applies to the classification for degrees of protection provided by enclosures for
electrical equipment with a rated voltage not exceeding 72,5 kV.
Note 2 to entry: E.g. environmental conditions can include effects of water or dust.
3.18
relevant authority
organization with appropriate statutory powers of control
[SOURCE: EN 16323:2014, definition 2.1.3.1]
3.19
cyclic design life
period of time applied in computational verifications for alternating or threshold loads
Note 1 to entry: The cyclic design life can be used for fatigue verifications.
Note 2 to entry: The cyclic design life is different from the warranty time, the design service life (see 3.12) and an
expected service life (see 3.14)
4 Abbreviated terms
For the purposes of this document, the following abbreviated terms apply.
MCC Motor control centre
DS Dry solids
5 Requirements
5.1 General requirements
Design and construction of wastewater treatment plants shall meet the following requirements:
a) compliance with discharge limits;
b) capability to satisfactorily treat the full range of flows and loads;
c) minimizing the Health, Safety and Wellbeing risks to all personnel;
d) elimination or management of nuisance, odour, noise, toxicity, aerosols and foam. Each shall meet
the relevant requirements according to EN 12255-9 and EN 12255-10;
e) during the design process reasonable consideration shall be given to the future expansion of the
facility to accommodate:
— inclusion of population growth;
— inclusion of likely changes in environmental discharge requirements (particularly air and water
quality);
— inclusion of the effects of climate change, e.g. increased risk from flooding and droughts;
— potential for change in legislation;
f) achievement of the expected service life and long-term structural integrity, including water and gas
tightness;
g) provisions shall be made for all operation and maintenance to be carried out safely;
h) asset supportability and logistic support considerations shall be integrated into the design of a
system or equipment to ensure the equipment is supported throughout its expected service life and
remains within performance requirements;
i) provision for future extensions or modifications of the plant shall be considered;
j) capability to deliver the requirements for Throughput, Reliability, Availability, Maintainability (T-
RAM);
k) should be cost effective in respect of total costs (capital and operating costs);
l) the energy consumption during construction and operation shall be considered;
m) the waste products shall be reduced in quantity and improved in quality as far as reasonably
achievable to allow for reuse or safe disposal.
NOTE National regulations can apply.
5.2 Design requirements
5.2.1 Resilience
The following requirements shall be considered during the design stage of a wastewater treatment plant
to ensure resilience:
a) all assemblies that are subject to occasional failure (e.g. pumps and compressors) shall be installed
with sufficient stand-by capacity so as to achieve full treatment capacity and efficiency with one
assembly out of service. In the case where stand-by assemblies cannot be practically installed,
provisions shall be made to replace rapidly by another one kept in stock;
b) in order to facilitate maintenance, repair or replacement, upstream and downstream isolation shall
be provided and it shall be possible to bypass every unit or assembly, either by a parallel unit or
assembly, channel or pipe
c) where necessary the inlet to the treatment plant shall include a facility which limits the flow. Such
facilities may be balancing tanks and/or stormwater overflows as required by the relevant
authorities;
d) where the primary power supply cannot be relied upon the need for a secondary power supply shall
be risk assessed including the likelihood of power interruption and shall consider historical
information and robustness of supply. The assessment of the probability of supply failure shall
include supply interruptions of any duration. The mitigating measures shall consider the operational
time to respond and the criticality of the process e.g. impact on compliance, risk of pollution or failure
to comply with the permit etc.
Where an application requires a secondary power supply, all other possible points of weakness in
the system (other than just the primary power source) that can impact on the treatment process shall
be identified. The selection of the most appropriate technology/solution to provide secondary power
shall be based on Whole Life Cost;
e) Motor control centres (MCC) that are identified as critical to the treatment process shall be provided
with a mobile generation point for the provision of secondary power under emergency/maintenance
conditions. Mobile generation shall be rated in line with the associated distribution transformer and
shall provide sufficient power directly to the consumer without the need for temporary distribution
equipment;
f) when the power supply is restored following an interruption, the treatment plant shall be designed
so that normal operating status is resumed as quickly as possible. This may require:
— automated sequential start-up of power consumers;
— manual inspections and interventions;
— onsite technical procedures and checks;
— organisational measures and permissions;
g) appropriate provision shall be made for the case of malfunction or emergency;
h) due consideration shall be given to providing resilience by designing systems with parallel units or
components, rather than designing large single-stream systems;
i) the number and skill level of available maintenance resources shall be considered when designing
units and defining the associated maintenance requirements. The security of supply for future
maintenance services and spares shall also be considered including the standardization and updating
of software to minimize the impact of operating obsolete equipment;
j) the design shall take into consideration the required operating regime and, in particular, allowance
shall be made for maintenance of equipment that is required to run 24 h a day, 7 days a week. The
design of equipment shall take into account the spares strategy and incorporate the appropriate
amount of redundancy. In order to permit maintenance, repair and replacement of process
equipment the designer shall consider the need for upstream and downstream isolation methods.
5.2.2 Safety and accessibility
The following requirements shall be considered during the design stage of a wastewater treatment plant
to ensure safety and accessibility:
a) The design shall enable operation, maintenance and cleaning to be carried out easily and safely (e.g.
access, flushing connections to pipes, isolation means).
b) Equipment shall be designed such that it can be easily delivered, installed, maintained, operated and
replaced. Structures shall have sufficient installation openings and lifting equipment (e.g. lifting
hooks or rails or a crane).
Common types of lifting systems are:
— overhead crane;
— gantry Crane;
— fixed monorail;
— 'A' Frame;
— jib crane;
— davit;
— mobile hoist;
— mobile crane.
c) Where large covers are used or other plant and equipment require the use of a mobile crane then a
suitable access road will be provided. Sufficient footprint for mobile cranes to park and operate and
an area for placing the covers shall be provided.
Covers shall contain sufficient openings and access hatches for routine operation and maintenance
to be carried out from outside.
The creation of confined spaces that require regular man- entry should be minimized.
Covers should be completely removable to provide the best possible access for personnel and
equipment.
d) A means of providing sufficient ventilation of the areas to be accessed shall be considered in the
design.
e) Instruments and equipment requiring adjustment or routine maintenance shall, wherever possible,
be accessible from ground level because working at height carries an increased risk to safety and the
provision of permanent above-ground access can be costly.
5.2.3 Other design requirements
The following requirements shall also be considered during the design stage of a wastewater treatment
plant:
a) Provision shall be made for taking representative samples upstream and downstream of each
process unit (including sludge treatment) and of any other flow whose characteristics are important
for operation and supervision e.g. return flows from various treatment processes.
b) The design shall ensure that all information (quantities and qualities) that is important for effective
operation of the plant (or to demonstrate compliance with regulatory requirement) is readily
obtainable e.g. flows, levels, pressures, temperatures, dissolved oxygen concentrations, pH-values.
c) For flow rate measurements, sufficiently long pre- and post-run distances shall usually be taken into
account. The specifications of the measurement technology manufacturers shall be taken into
account accordingly. For other measuring and sampling points, the possible influence on the
measurement result shall also be taken into account when choosing the installation location.
Accessibility to the measuring and sampling points shall be ensured. Measurement equipment should
be fitted in accordance with manufactures instructions.
d) Equipment shall, wherever possible, be obtained from manufacturers operating a suitable quality
system. Materials and manufactured articles shall, wherever possible, be certified for use in the EU
(CE sign). Recycled materials should be used where appropriate.
NOTE EN ISO 9001 is an example of a suitable quality system.
e) Off-site manufacturing opportunities shall be explored as alternatives to traditional on-site
construction for all aspects of the design from civil structures through to electrical equipment. Pre-
assembled components, units, pre-cast structures, packaged-plants and skid-mounted, pre-
fabricated assemblies delivered to site, shall be considered. These solutions offer many advantages
including safer construction environments, reduced project durations and reduced customer impact.
f) Buildings or enclosures to house process units and equipment should only be provided where there
is a requirement to provide security, protect assets against the elements, or where a safe
environment is required in order to carry out frequent or critical operating and maintenance
activities, or where planning constraints dictate or the containment of noise, dust, vibration or odour
is not achievable by other means.
g) The provision of permanent buildings for housing equipment is costly. However, when deciding
whether to provide a building it is necessary to balance cost against the need to ensure that
equipment is protected from the elements, can be attended to and maintained as necessary and does
not represent a source of nuisance from noise, odour or dust.
h) Decisions whether to build structures above or below ground shall be based upon lowest whole-life
cost. Factors such as pumping and waste disposal costs and planning and environmental constraints
shall be taken into consideration.
i) Where designing lifting solutions for use in the future maintenance of equipment, the decision
whether to install permanent lifting equipment or not should be based upon a whole-life cost
assessment that balances the capital cost of providing fixed equipment and its future replacement,
maintenance and inspection, against the ongoing operational cost of providing temporary equipment
at each intervention over the design life (requirements for minimum design life are given in Annex D,
D.6).
5.3 Modularity
Standby, redundancy and modularity shall be considered during the planning stage. The following
principles should apply:
a) standby units or equipment shall be provided where they are required for continuous operation of
the treatment plant;
b) where temporary failure of units or equipment is acceptable, consideration should be given to how
long it will take to repair or replace the equipment;
c) while heavy equipment cannot usually be replaced readily, small equipment should be kept in stock;
d) common equipment dimensions should be taken into consideration in order to enable competition
between manufacturers or suppliers;
e) structures (e.g. channels for screens) should be designed such that equipment from multiple
manufacturers or suppliers can be utilized;
f) equipment should be fitted into structures (e.g. tanks or vessels). Access for equipment and
component replacement shall be provided;
g) equipment should be replaceable with equipment from other manufacturers;
h) components of the equipment (e.g. motors, gearboxes and bearings) should be replaceable with
components from other suppliers;
i) equipment suppliers shall be asked during the planning stage to provide specifications and
dimensions of their equipment and also of integrated components (such as pumps, motors or
sensors);
j) connections should be designed such that they can be fitted with equipment or component
connections of several manufacturers.
5.4 Structural requirements
5.4.1 General
All structures shall be:
a) stable to bear all loads during construction, operation and maintenance periods, e.g. water pressures
and static and dynamic forces being induced by the equipment (requirements for design loads are
given in Annex D);
b) resistant to chemical and biological attack from wastewater, sludge, air and gas components and
against temperatures, temperature changes and climatic conditions as appropriate;
c) protected against flotation;
d) made for resisting vibration, frost protection and for odour and noise control;
e) designed such that the equipment can be easily delivered, installed, maintained, operated and
replaced. Structures shall have sufficient installation openings and lifting equipment (e.g. lifting
hooks or rails or a crane).
Flow splitting structures shall be designed such that the wastewater flow is proportionally distributed to
downstream treatment units and shall be effective across a wide range of flow rates.
5.4.2 Dimensional tolerances
The permissible dimensional tolerances for structures which are required for the function of the
equipment are specified in the relevant specific standards or Annex B. Other dimensional tolerances shall
be agreed with the supplier of the equipment.
5.4.3 Concrete tracks for travelling mechanical equipment (e.g. Scraper Bridges)
Requirements for wheels and tracks are given in Annex C.
5.4.4 Fixings and connections between equipment and structures
The possibility of differential settlement between structures, and between structures and equipment
(such as pipelines) shall be taken into account. Sufficient flexible joints and flexibility in the equipment
itself or in its connections to the structures shall be provided.
Reinforcement in the structure shall not be used for securing equipment.
To avoid galvanic corrosion, metals with a different electro-chemical potential shall be prevented from
coming into contact, e.g. by providing electrical insulation between them.
Where metallic fixings might be in electrical contact with the steel reinforcement of the structure,
appropriate electrical insulation shall be provided, e.g. insulating, chemical anchors with threaded rods.
Tanks for storage, batching or mixing of chemicals shall be designed to be attached to their foundations
and associated pipework, using readily available, removable components (e.g. base flanges, anchor
channels and tie bolts, standard detachable pipe couplings, flanged pipe connections). Wherever possible
such foundations shall have a flat surface for the tank to bear upon.
5.4.5 Safe access
The security of sites should be based on a principle of ensuring that sites have suitably secure boundary
fencing and entrance gates that are normally kept locked at all times. Access to the site shall be restricted
to authorized personnel and controlled through a ‘signing-in’ procedure.
Safe access in the form of paths, gangways, bridges, stages and the like shall be provided to allow
supervision, operating, servicing, cleaning and maintenance. Openings shall be provided which allow
easy replacement of equipment.
The location of operating and maintenance points shall allow for adverse weather conditions, other
hazards (e.g. handling of gases, vapours, sludge, oil and grease) and the possibility of structural failure
and the avoidance of squeeze and sheer points.
To determine the type of access required for a particular work area it will be necessary at the design stage
to examine all operating and maintenance activities that take place, including such activities as machine
operation and adjustment, taking of instrument readings or drawing of samples, filter replacement,
inspection of lifting equipment, cleaning of instrument probes, cleaning of windows, changing of light
bulbs, etc. A systematic process should be used to provide a particular focus on this key aspect of
workplace design.
Where vehicular access is anticipated, a hard area shall be provided that will be sufficient to take the
expected load.
Permanent access arrangements shall be provided where frequent access is required. Stairs are safer
than ladders and the preferred solution for permanent access to elevated work areas or for access
between floors and mezzanines is to provide a staircase rather than a fixed vertical ladder.
Access shall be provided in close proximity to the anticipated destination whilst also ensuring that the
access provides a safe area to stand. Situations where personnel need to stand on or traverse benching,
channels and equipment shall be avoided.
The need for working at height should be avoided wherever reasonably possible by locating equipment
such that operation, maintenance or inspection of that equipment can be carried out from a fixed
platform.
The buildings and access shall be sufficiently large to allow for all foreseeable erecting and dismantling,
maintenance and repair operations and replacement of assemblies in an easy manner.
Appropriate means shall be provided to deter access by unauthorised persons.
5.4.6 Building ventilation
In enclosed rooms, the possible existence of damp atmospheres, foul air and the risk of explosions shall
be considered according to EN 12255-10. Adequate ventilation shall be provided according to
EN 12255-9. If necessary, means for frost protection shall be provided.
5.4.7 Water supply and drainage
Where occasional flushing is required, a water supply shall be installed. Process water shall preferably
be used for this purpose. Appropriate means shall be provided to prevent process water from
contaminating the drinking water network.
Appropriate drainage shall be installed where water accumulation can occur due to overflow, leakage or
flushing. In such locations, all floors shall be sealed and sloped towards a pit from where the water drains
by gravity or is automatically pumped away.
All tanks (above or below ground) shall be designed and constructed to allow them to be emptied safely,
economically and with minimum disruption to adjacent or remaining process units.
5.4.8 Lifting equipment
Lifting equipment or adequate provisions for installation and removal shall be provided where necessary
in order to allow all maintenance work and replacement of all assemblies.
5.4.9 Storage and conveyance of hazardous chemicals and fuels
The onsite storage of hazardous chemicals and fuel should be minimized wherever possible. Where there
is no practical option other than to store or convey hazardous liquid, chemicals or fuels, provisions shall
be made to prevent environmental impact in case of leakage. EN 12255-10 and EN 12255-13 shall be
taken into account. The required safety provisions (e.g. double tank walls, tanks in bunds, leak sensors)
depend on the volumes stored and potential risks. The necessary protective measures are further
specified in national regulations.
Tanks containing chemicals that would interact to form a hazardous mixture or could attack the material
of other tanks shall not share a single bund.
NOTE National regulations can define chemicals that need to be prevented from contaminating water or
wastewater.
Leakage of some chemicals, e.g. precipitants, coagulants and flocculants, shall be prevented. Their
containers shall be placed in troughs which can withhold the entire container volume. Pipelines or hoses
conveying such chemicals shall be installed within protecting pipes conveying leaking fluid to a trough.
The troughs shall be equipped with a leak sensor providing an alarm.
5.5 Requirements for equipment
5.5.1 Principles for mechanical design
The use and requirements of the equipment shall be specified.
A general description and the following information shall be provided:
a) loads (e.g. traffic loads, wind loads, snow loads, operating loads and travelling single loads);
b)
...