Reference number  
RS 126-3: 2018  
© RSB 2018  
 
 
 RWANDA 
STANDARD  DRS  
126-3 
 
Second  edition  
2018 -mm-dd 
 
Wastewater treatment plants  
Part 3: 
Safety principles  
  DRS  126-3: 2018  
©RSB 2018 - All rights reserved                  ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB 2018  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized 
in any form or by any means, electronic or mechanical, including photocopying and microfilm, without 
prior written permission from R SB. 
Requests for permission to reproduce this document should be addressed to : 
Rwanda Standards  Board  
P.O Box 7099 Kigali -Rwanda  
KK 15 Rd, 49  
Tel. +250 788303492  
Toll Free: 3250  
E-mail: info@rsb.gov.rw  
Website: www.rsb.gov.rw   
ePortal: www.portal.rsb.gov.rw   DRS  126-3: 2018  
iii                ©RSB 2018 - All rights reserved  
 Contents  Page 
1 Scope  ................................ ................................ ................................ ................................ .............  1 
2 Normative references  ................................ ................................ ................................ ...................  1 
3 Terms and definitions  ................................ ................................ ................................ ..................  1 
4 General requirem ents ................................ ................................ ................................ ..................  2 
4.1 Confined spaces, hazards and warning systems  ................................ ................................ ..... 2 
4.2 Vehicular and pedestrian traffic routes  ................................ ................................ ......................  3 
4.3 Fixed ladders, manhole steps and staircases  ................................ ................................ ...........  5 
4.4 Falling preventions and covers  ................................ ................................ ................................ .. 5 
4.5 Emergency exits  ................................ ................................ ................................ ...........................  6 
4.6 Work p laces, work platforms and maintenance platforms  ................................ ......................  6 
4.7 Lifting equipment  ................................ ................................ ................................ .........................  6 
4.8 Ventilation  ................................ ................................ ................................ ................................ ..... 7 
4.9 Areas at risk from explosions  ................................ ................................ ................................ ..... 7 
4.10  Hygienic facilities  ................................ ................................ ................................ .........................  8 
4.11  General warning signs  ................................ ................................ ................................ .................  8 
5 Special requirements  ................................ ................................ ................................ ...................  9 
5.1 Systems for separating solids from wastewater  ................................ ................................ ....... 9 
5.2 Wastewater pumping stations  ................................ ................................ ................................ .. 10 
5.3 Aeration tanks  ................................ ................................ ................................ .............................  10 
5.4 Digestion tanks, low -pressure gasholders  ................................ ................................ ..............  11 
5.5 Digester gas pipes  ................................ ................................ ................................ ......................  11 
5.6 Desulphurizing plants  ................................ ................................ ................................ ................  11 
5.7 Gas engine rooms and gas engines  ................................ ................................ .........................  12 
5.8 Gas flares  ................................ ................................ ................................ ................................ .... 12 
5.9 Sludge dew atering  ................................ ................................ ................................ ......................  12 
5.10  Installations for storage and handling of chemicals and hazardous substances  ...............  13 
 DRS  126-3: 2018  
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 Foreword   
Rwanda Standard s are prepared  by Technical Committees and approved by R wanda Standards Board (RSB) 
Board  of Directors in  accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The main task of technical committees is to prepare national standards.  Final Draft Rwanda S tandards adopted 
by Technical committ ees are ratifie d by me mbers of RSB Board of Director s for publication and gazettment as 
Rwanda Standards.  
RS 126-3 was prepared by Technical Committee RSB/TC 013, Water and Sanitation  
In the preparation of this standard, reference was made to the following standard s: 
1) BS 12255 -10:2001 1085, Wastewater treatment plants. Safety principles  
The assistance de rived from the above source is hereby acknowledged with thanks.  
This second edition cancels and replaces the first  edition of RS 126-3: 2012, which  has been technically revised.  
RS 126 consists of the following parts, under the general title Wastewater treatment plants : 
 Part 1: Vocabulary  
 Part 2: General construction principles   
 Part 3: Safety principles   
 Part 4: General data required   
 
  DRS  126-3: 2018  
v                ©RSB 2018 - All rights reserved  
 Committee membership  
The followin g organizations were represented on the Technical Committee on Water and Sanitation  (RSB/TC 
013) in the preparation of this standard.  
Ministry of Environment (MoE)  
Ministry of Disaster Management and Refugee Affairs (MIDIMAR)  
Ruliba Clays Limited  
Shine Engineers Multisectoral Company Limited (SEMC Ltd)   
Sulfo Rwanda Industries (SULFO)  
University of Rwanda/College of Science and Technology (UR/CST)  
Water and Sanitation Corporation Ltd (WASAC Ltd)  
Rwanda Standards Board (RSB) – Secretariat  
 DRS  126-1: 2018  
1                ©RSB 2018 - All rights reserved  
 Waste water treatment plant — part 3: safety principles   
1 Scope   
This Rwanda Standard  defines safety requirements for wastewater treatment plants to be constructed or 
reconstructed for  the protection of employees involved in wastewater treatment process.  
2 Normative references  
The following referenced documents are indispensable for the app lication 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.  
RS 548 -1:2012 Wastewater Treatment -Part 1: Vocabulary.  
RS 548 -2:2012 Wastewater treatment plants –Part 2: General construction principles.  
3 Terms and definitions  
For the purposes of this standard, the following terms and definitions apply.  
3.1 
sewerage within a wastewater treatment plant  
all structures used for collecting, draining or storing of wastewater within a wastewater treatment plan t 
NOTE  Sewerage within a wastewater treatment plant includes:  
a) Open and closed channels;  
b) pumping stations;  
c) Storm water drainage and treatment systems.  
3.2 
wastewater treatment plant  
facilit y for the physical, biological and chemical treatment of wastewater inclusive of all facilities for the treatment 
of solid wastes (screenings, grit, and sludge)   
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 3.3 
confined spaces  
all structures of sewerage and wastewater treatment plants which are in con tact with the wastewater, sludge, 
hazardous chemicals, etc., as far as they are covered or sunken  
NOTE  Confined spaces also include inspection manholes and other shafts even if they are not in open contact with 
the wastewater.  
4 General requirements  
Complian ce with safety regulations shall be an integral part of the design, construction and operation  of the 
facilities . 
4.1 Confined spaces, hazards and warning systems  
4.1.1  Confined spaces  
Special consideration is required for confined spaces in wastewater treatment pla nts which include but not 
limited to : 
a) Conduits;  
b) Shafts, inspection manholes, seepage water shafts;  
c) Basins (covered or sunken);  
d) drop structures;  
e) Valve structures;  
f) Inlet and outlet structures;  
g) Sunken or enclosed screening plants;  
h) pumping stations (dry or wet  wells);  
i) Sludge silos and covered thickeners;  
j) Digestion tanks;  
k) Gasholders (gasometers);  
l) Completely covered plants.  DRS  126-1: 2018  
3                ©RSB 2018 - All rights reserved  
 4.1.2  Hazards  
Hazards from wastewater treatment plants can arise from solid substances, liquids, vapours, gases and bio -
aerosols, micro -organisms a nd dust particles in various  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. fermentatio n, putrefaction) or by chemical reactions (e.g. when different 
wastewaters are mixed). ~ 
4.1.3  Sources of hazards  
Hazards can arise from the following sources:  
a) Gases or vapours which can cause fires or explosions;  
b) Oxygen deficiency which can result in suffocatio n; 
c) Toxic, corrosive, irritant, flammable or hot substances, which can cause harm to health by contact, 
absorption ; 
d) Through the skin or by ingestion, inhalation, or penetration through puncture wounds;  
e) Increase of flow or level of water, e.g. following heav y rain or flooding;  
f) Micro -organisms and their metabolic products which can result in infections;  and 
g) Radioactive substances.  
4.1.4  Warning systems for the safety of persons  
Provision shall be made to enable monitoring the atmosphere in confined spaces before ent ering to make sure 
that no health risk for persons exists. Fixed or portable monitoring equipment may be employed; portable 
monitoring shall be operable from places of safety. Fixed monitoring equipment may also be used to actuate 
emergency systems (e.g. s witching 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 protected from 
explosion. There shall be means of communication, e.g. alarm syste ms, telephone or radio  at a wastewater 
treatment facility  
4.2 Vehicular and pedestrian traffic routes  
4.2.1  Vehicular and pedestrian traffic routes shall be laid out in accordance with the operational requirements 
to provide safe access to work places and easy maintenance.  
This requirement is adequately satisfied, if:  
a) Work places can be reached as directly and conveniently as possible;   
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 b) 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;  
c) Obstacles such as open channels or conveyor belts are bridged over;  
d) Floors are easy to clean;  
e) Floor coverings, gratings, roads and paths have non -slip surfaces, and collection of water on the surface s 
is prevented;  
f) Paths are constructed of materials which are resistant against wear and tear;  
g) Slabs and pavings are laid even and with narrow joints;  
h) Non-slip surfaces allow safe walking in every direction under adverse conditions;  
i) Doors of emergency exits  open to the outside.  
4.2.2  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.:  
a) Traffic routes are kept free from installations so that they  can be used at any time;  
b) 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 diversio n barriers or mirrors;  
c) 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;  
d) 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;  
e) 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;  
f) Speed limits of 20 km/h have been considered.  
4.2.3  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.  
4.2.4  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 4.3.1.  DRS  126-1: 2018  
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 4.3 Fixed ladders, manhole steps and staircases  
4.3.1  If steps or ramps are not possible for structural reasons, fixed ladders, step irons, staircases or other 
access facilities shall be provided.  
4.3.2  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. Ladders shall have a minimum d istance to the wall of 150 mm.  
4.3.3  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).  
4.3.4  Safety cages are not allowed in confined  spaces, where they may hinder the rescue of injured persons.  
4.3.5  Suitable access aids shall be provided above access points for climbing on and off safely.  
This requirement is adequately satisfied if e.g.:  
a) 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;  
b) Existing railings provide a handhold;  
NOTE: A man -riding winch can be used.  
4.3.6  Rest platforms shall be provided in maximum inte rval of 6 m on all steps or fixed ladders with a length 
of more than 10 m in such a way that the rescue of injured persons and the transport of tools and materials will 
not be hindered.  
4.3.7  The clearance on the user’s side of fixed ladders shall be not l ess than 0, 65 m for vertical ladders and 
not less than 1,1m for sloping ladders.  
4.4 Falling preventions and covers  
4.4.1  Work places and traffic routes adjacent to a vertical drop or other dangerous areas shall have 
permanent guardrails to prevent persons fa lling 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 basis tensioned chains, ropes or nets m ay be used.  
4.4.2  Suitable protection against falling is provided e.g. by a minimum of 1 .1 m high permanently fixed railings 
or enclosing walls.  
4.4.1  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 in termediate 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.   
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 4.4.1  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 protectiv e 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.  
4.4.1  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.  
4.4.2 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.  
4.4.3  Covers shall  be handled safe, protected against unintentional displacement and shall withstand the 
operational and climatic stresses.  
This requirement is adequately satisfied if e.g.:  
a) Covers can be opened from safe standing positions;  
b) Hinged covers can be secured in t he open position;  
c) Heavy covers are additionally equipped with counterbalances, hydraulically actuated lifting devices or  
d) Pneumatic springs.  
4.5 Emergency exits  
Tanks shall be equipped with permanently installed emergency exits in every self -contained basin section.  
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. ropes) for assisting climbing out.  
4.6 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 part ies. 
The requirement for non -slipperiness also includes the requirement that gratings and standing positions shall 
where possible be located safe from flooding.  
4.7 Lifting equipment  
Suitable and sufficient lifting equipment shall be available for the handling  of heavy loads.  DRS  126-1: 2018  
7                ©RSB 2018 - All rights reserved  
 This requirement is adequately satisfied if e.g.:  
a) A lifting device is installed;  
b) A support for a mobile hoist is built in;  
c) A tripod and portable lifting hoist are used with safety devices to prevent the legs shifting or splaying out;  
d) An ad equate standing area is available, designed in size and in load -bearing capacity for a vehicle with  
e) Pivoted and telescopic jib (crane boom);  
f) Safe use is possible of multi -purpose lifting appliances, e.g. equivalently equipped lorry -mounted lifting  
g) Devices,  forklift trucks, small hydraulic excavators, etc.  
4.8 Ventilation  
Confined spaces in wastewater treatment plants, in which dangerous substances, explosive atmosphere or 
aerosols can accumulate in the breathing air in concentrations 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 from a safe position. Natural ventilation can be effective, if e.g. the design of the opening provides 
sufficient ven tilation 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 effective means of ventilation. 
Forced ventilation shall be provided if natu ral ventilation is not sufficient.  
4.9 Areas at risk from explosions  
4.9.1  Danger of explosions in wastewater -systems can arise e.g. by illegal introduction of inflammable 
substances or by anaerobic degradation processes, e.g. methane from sludge digestion. Co nfined spaces in 
wastewater treatment plants shall be constructed and equipped in such a way as to prevent the formation of an 
explosive atmosphere. If it is not possible to prevent the formation of an explosive atmosphere, the ignition of 
explosive atmosp heres shall be prevented by additional protective means, e.g. ventilation or permanent 
installation of gas warning devices to initiate emergency procedures.  
Permanent gas warning devices should have pre -set concentrations, e.g.:  
a) At 20 % lower explosive limit (LEL) preliminary alarm (e.g. switching on the technical ventilation, opening of 
Doors);  
b) At 50 % LEL initiation of emergency functions (e.g. switching off ignition sources. Areas of wastewater 
treatment plants with explosion hazards shall be clearly marked and access to them shall be prevented 
except for authorized workers. Structural measures can limit the areas at risk from explosion. Structural 
measures include e.g. adequately gas -tight walls made of non -combustible material and gas -tight ducts 
and conduits. Brick walls plastered on both sides and reinforced concrete walls are sufficiently gas -tight in 
this sense. Rooms above ground level, where an explosive atmosphere may arise under exceptional 
circumstances, shall be isolated from adjoining rooms  by automatically shutting gas -tight doors.   
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 Explosion prevention measures which prevent the emergence of explosive atmosphere shall generally be 
considered in the early design stage.  
4.9.2  Traffic routes for motor vehicles shall be located outside areas wh ere explosion hazards may exist.  
4.10 Hygienic facilities  
The extent to which hygienic facilities are necessary will depend upon the size and location of the treatment 
plant.  
These should include:  
a) washing protective clothing including shoes and boots;  
b) Personal washing (hand -basins and showers);  
c) eating of meals and preparation of beverages;  
d) Storage of personal effects;  
e) First aid materials.  
Some facilities may be provided on a vehicle and others on a suitable location.  
4.11 General warning signs  
Signs indicating warnin gs should be placed well visible at all entrances of areas with increased risk, e.g.:  
a) Electrical hazards;  
b) High noise level;  
c) Automatically operated moving equipment;  
d) Presence of dangerous gases and possible explosion hazard;  
e) Oxygen deficiency;  
f) Hazardous che micals.  
Signs indicating an obligation or requirement shall be placed at the entrance of the appropriate areas, e.g.:  
a) No smoking;  DRS  126-1: 2018  
9                ©RSB 2018 - All rights reserved  
 b) Use of safety glasses;  
c) Use of hard hats;  
d) Use of ear protection;  
e) Use of escape or full breathing apparatus;  
f) permit to work requirements.  
Signs referring to safety and fire preventing equipment shall have information directing to the equipment 
location,  
e.g.: 
a) Emergency exits;  
b) Fire extinguishers;  
c) rescue equipment;  
d) First aid boxes.  
5 Special requirements  
5.1 Systems for separating soli ds from wastewater  
5.1.1  Screening and filtration equipment and installations for dewatering the screenings as well as grit 
chambers and grease traps shall be designed so as to minimize contact by persons with the solids and to ensure 
safe removal of the s olids.  
5.1.2  In aerated grit chambers with spiral flow and water depths exceeding 1,35 m, a suitable holding fixture 
for self -rescue shall be provided on the downward flow side over the whole length of the chamber.  
Safety ropes or bars shall be installed at the water level around rotating equipment. In aerated grit chambers 
with horizontal flow, emergency exits should be installed downstream.  
These emergency exits shall not be located in the vicinity of the grit hoppers and shall be within reach of the 
holding fixture. Suitable holding fixtures for self-rescue  can be for example, grippable pipes, stay bars or tightly 
stretched cables.  
5.1.3  Sunken loading bays for vehicle containers shall be equipped on the approach side with a raised edge 
to Prevent the ve hicle wheels falling in when reversing. A suitable raised edge would be a barrier a minimum of 
0, 25 m high painted in yellow/black contrasting colours.   
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 5.2 Wastewater pumping stations  
5.2.1  In order to avoid hazards from dangerous substances, wet wells shall only have access from outside of 
the buildings and are not allowed to be connected with other rooms.  
5.2.2  Permanent provision for man entry to wet wells is not required if there is no need for man entry either 
for Cleaning or maintenance purposes.  
Access is not required if e.g. the deposition of solids is prevented by mechanical equipment or if cleaning and 
Maintenance work can be carried out effectively from safe standing places.  
5.2.3  Pumps even when installed in wet wells and electrical equipment shall be so designed, that ignition 
energy can be released if they are used in locations where explosion hazards may occur. This requirement is 
adequately satisfied, if e.g. explosion -protected submersible motor -pumps are used, or if the pump motors are 
complete ly submerged during the whole pumping cycle.  
5.2.4  Pumps shall be designed and installed so that they can be maintained easily and safely. Each pump 
shall be capable of being hydraulically isolated while other pumps of the station are still operating. In t he case 
of screw pumps in addition it shall be taken into account that:  
a) The screw can be cleaned safely;  
b) The standing places over the inlet are situated clear of the highest water level.  
5.3 Aeration tanks  
5.3.1  Aeration and mixing devices shall be so designed  that maintenance work can be carried out safely.  
This requirement is adequately satisfied if e.g.:  
a) In basins equipped with compressed air aeration the aeration equipment can be lifted or swivelled  out of 
the Liquid; or  
b) Basins can be emptied for maintenanc e purposes.  
5.3.2  Surface aerators and mechanical mixing devices shall be equipped with emergency shut -offs. These 
emergency shut -offs shall be located next to the aeration or circulating devices and be within easy reach.  
Depending on the arrangement of su rface aerators or mechanical mixing devices (flow generators), one or more 
emergency shut -offs may be required.  
5.3.3  In aeration tanks with spiral flow and water depths exceeding 1,35 m, a suitable holding fixture for self -
rescue shall be provided on the downward flow side over the whole length of the tank.  
Safety ropes or bars should be installed at the water level around horizontal rotors. In aeration tanks emergency 
exits should be installed.  DRS  126-1: 2018  
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 5.4 Digestion tanks, low -pressure gasholders  
5.4.1  Digestion tank s and low -pressure gasholders shall be equipped with frost -protected devices to prevent 
the pressure exceeding the maximum or falling below the minimum permissible operating pressure.  
The pressure safety devices shall be designed to reset automatically or to give an alarm to a monitoring in case 
of low pressure.  
5.4.2  There shall be a minimum of two man entry points one above ground level and the other on the top. 
One of the man entry points to the digestion tanks shall have a minimum clear width of 0, 8 m.  
5.5 Digester gas pipes  
5.5.1  Pipes and fittings carrying digester gas shall be designed to withstand the mechanical, chemical and 
thermal stresses to be expected in operation.  
The requirement for mechanical and chemical durability is adequately satisfied, e.g . by suitable materials such 
as stainless steel.  
Mechanical stresses due to subsidence, temperature differences and vibrations are to be absorbed by suitable 
structural design of the pipelines, e.g. pipe loops or installation of extension compensating mem bers.  
5.5.2  Pipes  carrying digester gas shall be equipped with shut -off devices at the digester tank and before the 
gasholder.  
5.5.3  Pipes carrying digester gas shall be equipped upstream of gas consuming devices, desulphurizers and 
Suction pipes of compre ssors with fittings to prevent an unintended extension of flames. These can be, for 
example, flame arrestors or shut -off devices with flow measurement equipment. The effectiveness of the 
equipment must be confirmed against national regulations.  
5.5.4  Pipes  carrying digester gas which lead into enclosed rooms shall be equipped with shut -off devices 
situated in safe places outside these rooms.  
5.5.5  Facility  shall be provided for the safe discharge of condensate occurring in digester gas systems.  
This requirement is adequately satisfied by e.g.:  
a) Automatic condensate discharge systems;  
b) Locks with double shut -off fittings.   
Digester gas pipes should be clearly identified.  
5.6 Desulphurizing plants  
Desulphurizing plants shall comply with the gas safety equipme nt. In addition,  arrangements shall be made to 
ensure that:   
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 a) Air cannot enter the digester gas pipe and digester gas cannot enter the air pipe;  
b) The air supply is interrupted before a dangerous explosive atmosphere can develop;  
c) the temperature of the gas in the desulphurizing tank does not exceed 60 °C.  
5.7 Gas engine rooms and gas engines  
5.7.1  Gas engine rooms shall be provided with sufficient natural or forced ventilation  
5.7.2  Gas engine rooms and air intake pipes of gas engines shall be so constructed that no gas can enter 
during operation or in the event of faults. This requirement is adequately satisfied if e.g.:  
a) When the gas engine stops no gas can escape into the engine room. This can be achieved by installing an  
b) Automatic gas shut -off valve (with redund ant control);  
c) Crankcase ventilating pipes are led into the open air or the exhaust gases are reinjected into the closed  
d) System;  
e) Ventilation openings to gas engine rooms are not located near crankcase ventilating pipes or the entrance 
of 
f) Air suction or exha ust pipes of gas engines;  
g) Air suction pipes of gas engines are led in from outside.  
5.7.3  The ignition system of gas engines shall remain inactive until engine and exhaust system have been 
adequately flushed with air.  
5.8 Gas flares  
Gas flares shall be constructed and positioned in such a way that persons are not at risk by gases, flames or 
hot components. Gas flares shall be equipped with automatic ignition devices, flame arrestors and flame 
monitoring equipment.  
5.9 Sludge dewatering  
5.9.1  Sludge dewaterin g plants, in which gases and vapours can accumulate in noxious concentrations, shall 
be equipped with effective ventilation devices to exhaust gases and vapours from the source. During sludge 
dewatering, hazardous gases such as ammonia, hydrogen sulphide o r methane may be produced depending 
on the process or conditioning method. Hazardous gases may continue to be produced by dewatered sludge. 
Thus, rooms in which dewatered sludge is stored shall be well ventilated.  
5.9.2  Mechanically operated sludge dewater ing plants should be fitted with automatic cleaning equipment.  DRS  126-1: 2018  
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 5.10 Installations for storage and handling of chemicals and hazardous substances  
Systems for the delivering, filling, storage, mixing and addition of chemicals and hazardous substances shall be 
designed so that there is no risk to persons or the environment from liquids, gases, vapours and dust. This 
requirement is adequately satisfied if e.g.:  
a) The surface of the area where the chemical is delivered and transferred to facilities is sealed and the  
b) System is designed so that accidental spills can be recovered without danger;  
c) Tanks containing chemicals are made of adequately resistant material, connections for filling and  
d) Discharging are tight -sealing and the filling level and nature of the contents can  be checked from the  
e) Outside, overfilling can be reliably prevented, leaking liquids can be collected safely (collecting bunds,  
f) double -walled tanks or containments) and the correct safety code is marked on the outer walls of tanks   or 
Access doors to stor age rooms;  
g) Lime silos and their filling and extraction equipment are of dust -tight construction and are marked      clearly;  
h) Lime -milk mixing systems are tightly sealed and inspection holes cannot be opened during the mixing  
i) Process;  
j) A self-closing  and locking security cabinet is available for the storage of small quantities of combustible,  
k) Fire-assisting or toxic or corrosive hazardous substances at the work place (laboratories, workshops);  
l) Separate lockable storage rooms with safety equipment (e.g . fire and explosion protection, ventilation    and 
Means for collecting leakages) and adequate safety marking are available for the storage of larger  
m) Quantities of hazardous substances (e.g. lime, corrosive substances) as used in operating wastewater  
n) Treatment plants;  
o) Provisions are made to prevent environmental impact in case of leakage. A second emergency  
p) Containment shall be provided (e.g. double underground pipes, double tank walls, tanks in bunds which  
Have a minimum capacity of 110 % of the single la rgest tank) and sensors shall be installed which provide an 
alarm when the first containment is leaking . 
.  
©RSB 2018 - All rights reserved                  2 
  DRS  126-1: 2018  
ICS 13.030.20  
 
 
©RSB 2018 - All right s reserved