CEN/TR 16829:2016+AC:2019
(Main)Fire and explosion prevention and protection for bucket elevators
Fire and explosion prevention and protection for bucket elevators
This European Technical Report applies to bucket elevators that may handle combustible products capable of producing potentially explosive atmospheres of dust or powder inside the bucket elevator during its operation. The precautions to control ignition sources will also be relevant where the product in the bucket elevator creates a fire risk but not an explosion risk.
For the purposes of this report, a bucket elevator is defined as an item of bulk material handling equipment that carries material in powder form or as coarse products such as whole grain, wood chips or flakes, in a vertical direction by means of a continuous movement of open containers.
This Technical Report specifies the principles of and guidance for fire and explosion prevention and explosion protection for bucket elevators.
Prevention is based on the avoidance of effective ignition sources, either by the elimination of ignition sources or the detection of ignition sources.
Explosion protection is based on the application of explosion venting, explosion suppression or explosion containment and explosion isolation rules specifically adapted for bucket elevators. These specific rules may be based on agreed test methods.
This European Technical Report does not apply to products that do not require atmospheric oxygen for combustion.
Brand- und Explosionsschutz für Becherwerke
Dieser Europäische Technische Bericht gilt für Becherwerke, mit denen brennbare Produkte gehandhabt werden können, die während des Betriebs des Becherwerks zur Entstehung von explosionsgefährdeten Atmosphären aus Staub oder Pulver im Inneren des Becherwerks beitragen können. Die Schutzmaßnahmen zur Kontrolle von Zündquellen sind auch dann relevant, wenn das Produkt in einem Becherwerk eine Brandgefahr, jedoch keine Explosionsgefahr darstellt.
Für die Anwendung dieses Berichts wird ein Becherwerk definiert als eine Einrichtung zur Handhabung von Schüttgütern, in dem Material in Pulverform oder grobkörnige Produkte wie Getreide, Holzspäne oder Hackschnitzel in vertikaler Richtung durch kontinuierliche Bewegung von offenen Bechern transportiert werden.
Dieser Technische Bericht legt die Grundsätze und Richtlinien zur Brand- und Explosionsverhütung sowie zum Explosionsschutz für Becherwerke fest.
Verhütung basiert auf der Vermeidung von effektiven Zündquellen entweder durch die Beseitigung oder Erkennung der Zündquellen.
Explosionsschutz basiert auf der Anwendung von speziell für Becherwerke angepassten Regeln für Explosionsdruckentlastung, Explosionsunterdrückung oder explosionsfester Bauweise bzw. Explosions-entkoppelung. Diese spezifischen Regeln können auf vereinbarten Prüfverfahren basieren.
Dieser Europäische Technische Bericht gilt nicht für Produkte, die zur Verbrennung keinen Luftsauerstoff benötigen.
Prévention et protection contre l'incendie et l'explosion des élévateurs à godets
Le présent Rapport technique européen s'applique aux élévateurs à godets pouvant véhiculer des produits combustibles capables de générer des atmosphères explosibles de poussière ou de poudre à l'intérieur de l'élévateur à godets pendant son fonctionnement. Les mesures de contrôle des sources d'inflammation seront également pertinentes lorsque le produit manutentionné par l'élévateur à godets crée un risque d'incendie, mais pas un risque d'explosion.
Pour les besoins du présent rapport, un élévateur à godets est défini comme un élément d'équipement de manutention transportant un matériau en poudre ou sous forme de produits grossiers, tels que des grains entiers, des copeaux ou des pellets de bois, dans une direction verticale au moyen d'un mouvement continu de récipients ouverts.
Le présent Rapport technique spécifie les principes et les lignes directrices relatifs à la prévention de l'incendie et de l'explosion et à la protection contre l'explosion des élévateurs à godets.
La prévention est basée sur l'absence de sources effectives d'inflammation, par l'élimination des sources d'inflammation ou par la détection des sources d'inflammation.
La protection contre l'explosion est basée sur l'application de règles de décharge d'explosion, de suppression de l'explosion ou de confinement de l'explosion et de règles d'isolement de l'explosion spécifiquement adaptées aux élévateurs à godets. Ces règles spécifiques peuvent être basées sur des méthodes d'essai convenues.
Le présent Rapport technique européen ne s'applique pas aux produits qui ne nécessitent pas l'oxygène de l'air pour leur combustion.
Preprečevanje in eksplozijska zaščita korčnih elevatorjev pred požarom in eksplozijo
To evropsko tehnično poročilo se uporablja za korčne elevatorje, ki lahko prevažajo gorljive proizvode, ki lahko ustvarijo potencialno eksplozivne atmosfere prahu ali praška znotraj korčnega elevatorja med njegovim delovanjem. Previdnostni ukrepi za nadzor virov vžiga se uporabljajo tudi, kadar zaradi proizvoda v korčnem elevatorju obstaja nevarnost požara, vendar ne nevarnost eksplozije.
Za namene tega poročila je korčni elevator opredeljen kot del opreme za rokovanje z razsutim materialom, ki prevaža razsuti material v obliki prahu ali grobih delcev, npr. cela zrna, lesni sekanci ali kosmiči, v navpični smeri z neprekinjenim premikanjem odprtih vsebnikov.
To tehnično poročilo določa načela in smernice za preprečevanje požara in eksplozije ter eksplozijsko zaščito korčnih elevatorjev.
Preprečevanje temelji na preprečevanju dejanskih virov vžiga z odstranitvijo virov vžiga ali njihovim odkrivanjem.
Eksplozijska zaščita temelji na razbremenitvi tlaka eksplozije, zadušitvi ali zadržanju eksplozije in pravilih za izolacijo eksplozije, ki so posebej prilagojena korčnim elevatorjem. Ta posebna pravila lahko temeljijo na sprejetih preskusnih metodah.
To evropsko tehnično poročilo se ne uporablja za proizvode, ki ne potrebujejo atmosferskega kisika za zgorevanje.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-julij-2019
Preprečevanje in eksplozijska zaščita korčnih elevatorjev pred požarom in
eksplozijo
Fire and explosion prevention and protection for bucket elevators
Brand- und Explosionsschutz für Becherwerke
Prévention et protection contre l'incendie et l'explosion des élévateurs à godets
Ta slovenski standard je istoveten z: CEN/TR 16829:2016+AC:2019
ICS:
13.220.20 Požarna zaščita Fire protection
13.230 Varstvo pred eksplozijo Explosion protection
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
CEN/TR 16829:2016+AC
TECHNICAL REPORT
RAPPORT TECHNIQUE
April 2019
TECHNISCHER BERICHT
ICS 13.220.40; 13.230; 53.040.10
English Version
Fire and explosion prevention and protection for bucket
elevators
Prévention et protection contre l'incendie et Brand- und Explosionsschutz für Becherwerke
l'explosion des élévateurs à godets
This Technical Report was approved by CEN on 13 July 2015. It has been drawn up by the Technical Committee CEN/TC 305.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey 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
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 16829:2016+AC:2019 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 5
4 Bucket elevators . 6
4.1 General . 6
4.2 Bucket elevator types . 6
5 Fire and explosion hazards. 6
5.1 General . 6
5.2 Explosion hazards . 7
5.2.1 Presence of explosive atmospheres . 7
5.2.2 Presence of potential ignition sources . 8
5.2.3 Effect of ignition: smouldering product, fire, explosion, propagation of explosion . 10
5.2.4 Risk assessment . 10
5.3 Fire hazards . 10
6 Fire and explosion prevention and protection of bucket elevators . 11
6.1 General . 11
6.2 Fire prevention and protection . 12
6.2.1 Fire prevention . 12
6.2.2 Fire protection . 12
6.3 Explosion prevention and protection . 13
6.3.1 Prevention of explosive atmospheres . 13
6.3.2 Prevention of ignition sources . 14
6.3.3 Protective measures . 19
7 Information for use . 19
7.1 Markings . 21
Annex A (informative) Examples/types of bucket elevators . 22
Annex B (informative) Guidance on explosion venting . 28
Annex C (informative) Guidance on explosion suppression . 33
Annex D (informative) Example of an ignition hazard assessment . 36
Annex E (informative) Example of a nameplate . 61
Annex F (informative) Guidance for assessing the probability of generating explosive
atmospheres . 62
Bibliography . 63
European foreword
This document (CEN/TR 16829:2016+AC:2019) has been prepared by Technical Committee
CEN/TC 305 “Potentially explosive atmospheres – Explosion prevention and protection”, the secretariat
of which is held by DIN.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document includes Corrigendum 1 issued by CEN on 24 April 2019.
The start and finish of text introduced or altered by corrigendum is indicated in the text by tags
˜ ™.
1 Scope
This European Technical Report applies to bucket elevators that may handle combustible products
capable of producing potentially explosive atmospheres of dust or powder inside the bucket elevator
during its operation. The precautions to control ignition sources will also be relevant where the product
in the bucket elevator creates a fire risk but not an explosion risk.
For the purposes of this report, a bucket elevator is defined as an item of bulk material handling
equipment that carries material in powder form or as coarse products such as whole grain, wood chips
or flakes, in a vertical direction by means of a continuous movement of open containers.
This Technical Report specifies the principles of and guidance for fire and explosion prevention and
explosion protection for bucket elevators.
Prevention is based on the avoidance of effective ignition sources, either by the elimination of ignition
sources or the detection of ignition sources.
Explosion protection is based on the application of explosion venting, explosion suppression or
explosion containment and explosion isolation rules specifically adapted for bucket elevators. These
specific rules may be based on agreed test methods.
This European Technical Report does not apply to products that do not require atmospheric oxygen for
combustion.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
˜EN 1127-1™, Explosive atmospheres — Explosion prevention and protection — Part 1: Basic
concepts and methodology
EN 13237, Potentially explosive atmospheres — Terms and definitions for equipment and protective
systems intended for use in potentially explosive atmospheres
EN 13463-1, Non-electrical equipment for use in potentially explosive atmospheres — Part 1: Basic
method and requirements
EN 13463-5, Non-electrical equipment intended for use in potentially explosive atmospheres — Part 5:
Protection by constructional safety ‘c’
EN 13463-6, Non-electrical equipment for use in potentially explosive atmospheres — Part 6: Protection
by control of ignition source ‘b’
EN 14373, Explosion suppression systems
EN 14460, Explosion resistant equipment
EN 14797, Explosion venting devices
EN 14491, Dust explosion venting protective systems
EN 15089, Explosion isolation systems
EN ISO 12100, Safety of machinery — General principles for design — Risk assessment and risk reduction
(ISO 12100)
ISO 281, Rolling bearings — Dynamic load ratings and rating life
IEC/TS 60079-32-1, Explosive atmospheres — Part 32-1: Electrostatic hazards, Guidance
VDI 2263-1, Dust fires and dust explosions; hazards, assessment, protective measures; test methods for the
determination of the safety characteristic of dusts
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 13237, EN 15089 and the
following apply.
˜NOTE™ The zones for the classification of hazardous areas are defined in Directive
1999/92/EC.
3.1
volume
3.1.1
bucket elevator leg volume
internal volume of pipe section connecting head to the boot
3.1.2
bucket elevator head volume
internal volume above the leg connection, including outlet section and excluding the volume of the
pulley
Note 1 to entry: Attached chutes are not included.
3.1.3
bucket elevator boot volume
internal volume below the leg connection, including inlet section and excluding the volume of the pulley
3.2
vent spacing
distance between vents measured from centre to centre
3.3
bucket spacing
distance between buckets measured from centre to centre
3.4
combustible dust
finely divided solid particles, 500 μm or less in nominal size, which may be suspended in air, may settle
out of the atmosphere under their own weight, which can burn or glow in air, and may form explosive
mixtures with air at atmospheric pressure and normal temperatures
4 Bucket elevators
4.1 General
Bucket elevators are described as bulk materials handling equipment, conveying material in a vertical
direction by means of a continuous movement of open containers. A bucket elevator consists of three
main parts: the boot where the material enters the equipment, the leg or legs where the material is
transported upwards and the head where the material is discharged. The most common type of bucket
elevators generally use open containers fixed to a moving belt or chains. In case of a single leg bucket
elevator the belt moves upwards and returns in the same leg. In a twin-leg bucket elevator the
returning of the belt occurs in a second leg.
Bucket elevators require special attention since they have been involved in dust explosions and they
have many potential ignition sources. The most common ignition sources are due to mechanical
problems, for example due to friction between the belt and the casing, heating up of mechanical rotating
parts on elevator head and boot, impact of damaged buckets or foreign objects. These mechanical
problems may also create explosive atmospheres: impact or vibrations will cause dust deposits in the
legs to fall down and create an explosive atmosphere. Therefore if, during normal operation, there is no
explosive dust-air mixture present inside a bucket elevator, mechanical problems are still likely to
cause an explosion.
NOTE Maintenance related ignition sources like hot work are also very common.
Even if an ignition source does not cause an explosion it may result in a fire and spread quickly because
the leg of a bucket elevator acts as a chimney.
Fire and explosion protection of bucket elevators requires special attention. A bucket elevator might be
considered as two volumes (head and boot) between which there are one or two long ducts (the legs).
The information (see EN 14491) for flame accelerations inside a long duct, however, cannot be applied.
The buckets do affect flame acceleration: especially metal buckets which will cool the flame (and reduce
flame acceleration). But the buckets also form repeated obstacles which cause increased turbulence and
hence promote flame accelerations. Plastic buckets may become part of the fuel for a fire.
4.2 Bucket elevator types
There are many types of bucket elevators. Casing types include twin leg, single leg, and “Z” type. The
buckets can be attached to either a belt or a chain and can be made from metal or plastic.
Typical examples of the different types of bucket elevators are included in Annex A.
The Technical Report will focus on vertical bucket elevators. Z type bucket elevators operate at low
velocities and thus reduced dust generation and risk of ignition. Measures can be reduced in this case
and will not be dealt with in the following.
5 Fire and explosion hazards
5.1 General
A fire or explosion inside a bucket elevator is a large hazard due to the flame and/or pressure effects to
the surroundings which may lead to damage to the bucket elevator itself and can lead to damage to the
connected equipment, surroundings of the equipment and to personnel.
Consequences of ignition can be a smouldering fire, fire with flames, explosion and a propagating
explosion. Following a dust explosion a fire is likely to continue inside or outside the bucket elevator.
If an explosion occurs inside a bucket elevator, it will tend to accelerate, because of the large L/D ratio.
Without adequate protection this may cause failure of the bucket elevator and endanger the
surroundings: adjacent equipment, buildings and personnel.
When no precautions are included to prevent fire propagation, a highly hazardous situation can occur
where a fire or explosion may spread to adjacent sections of the installation, such as silo cells. With
explosion propagation, increased turbulence, pre-compression and jet ignition may trigger very violent
secondary explosions in these installations.
For a fire or an explosion to occur the following conditions must coincide:
— combustible dust is either deposited or whirled up within the explosion limits;
— sufficient presence of oxygen;
— an effective ignition source.
In bucket elevators the explosion hazard depends very strongly on the bulk material conveyed. In
particular the fine fraction of the bulk material with particle sizes less than 500 μm and the dustiness
(how easy a dust cloud is formed) play a decisive role here.
If a bulk material contains relevant fractions of dust, an explosion hazard is to be assumed.
Even in the case of low dust concentrations, in time dust can adhere to the bucket elevator casing
forming layers inside the bucket elevator that can be a few mm thick. The adhered dust layers are not in
themselves explosive mixtures but do form a continuous potential for an explosive mixture: e.g. due to a
malfunction of a bucket elevator (belt misalignment) the casing may start vibrating and the adhered
dust could become whirled-up and dispersed as an explosive dust cloud.
5.2 Explosion hazards
5.2.1 Presence of explosive atmospheres
The possibility of formation of an explosive atmosphere is very dependent on the product involved and
operational conditions either running full or empty.
˜NOTE External explosive atmospheres can also influence the atmosphere in the elevator.™
˜For example the following situations can exist:™
Example A Example B
The bucket elevator is conveying a combustible The bucket elevator is conveying a coarse product
product with an average particle size smaller than (typically > 1 000 microns) with a very limited amount
500 μm or a dusty product containing a considerable of fines.
amount of fines (here fines are defined as particles less
For this situation it is assumed that a potential
than 100 μm).
explosive atmosphere is likely to occur occasionally
This implies that during normal operation dust during normal operation.
clouds may arise frequently inside the bucket elevator
and are likely to be above the lower explosion limit
(LEL).
For this situation it is assumed that a potential
explosive atmosphere is frequently present.
The process conditions and specific product properties like moisture content, friability, granulometry,
flow characteristics and impurities will influence the occurrence of explosive atmospheres A or B.
In both situations dust can stick to the inner surfaces of the bucket elevator. Such dust deposits can
pose a fire hazard depending on the burning characteristics. In time these dust layers may accumulate
sufficient quantity of material to form an explosive atmosphere should they become dispersed by the
action of vibration, shaking etc. For most situations a layer with a thickness of 0,1 mm is sufficient to
create a potential explosive atmosphere. Since vibrations and other mechanical movements can be
expected, those dust layers can be disturbed to create a potential explosive atmosphere.
Only for a specific application, where it can be proven that no hazardous dust deposits will be created, a
zone 22 situation could be considered.
Note that inside a bucket elevator transporting a coarse granular product, due to friction of the product
granules, dust may be formed.
Typical examples are given in Annex F
5.2.2 Presence of potential ignition sources
5.2.2.1 General
A list of ignition sources can be found in EN 1127-1. An ignition hazard assessment should be carried
out by the manufacturer according to EN 13463-1.
This will identify the equipment related ignition sources able to ignite an explosive atmosphere
(potential ignition sources) and the effective ignition sources depending on the frequency of occurrence
i.e. in normal operation, expected malfunction or rare malfunction.
There are also ignition sources related to other influences:
— Ignition sources introduced from connected equipment have to be considered by the end user.
Typical examples are hot, glowing and burning product, embers, explosion from connected
equipment etc.
— External ignition sources due to smoking, maintenance, welding, cutting etc. (hot work) have to be
considered by the end user. These should be prevented by organizational measures.
— Ignition sources that may arise from the product conveyed should be taken into account: e.g. by
self-heating in deposits inside the bucket elevator.
Note that outside a bucket elevator, ignition sources can also be created by the bucket elevator as an
assembly: especially due to the presence of electrical equipment, drive systems and bearings. If the
bucket elevator is intended to be used in a potential explosive atmosphere the manufacturer has to
consider these ignition sources too and follow the standards EN 13463 series for non-electrical and
EN 60079 series for electrical equipment.
5.2.2.2 Equipment related ignition sources
Table 1 summarises the typical equipment related potential ignition sources that can be created
inside a bucket elevator.
Table 1 — Equipment related potential ignition sources
Potential ignition source Possible causes
Hot surfaces • Friction of bucket elevator belt against elevator casing wall due to
misalignment
• Friction between elevator belt and drive pulley due to slippage
• Friction of loose parts in bucket elevator (loose bucket, lost parts of
pulley lagging etc.) with moving parts
• Damage to bearings and gear units
Potential ignition source Possible causes
Mechanical sparks • Mechanical sparks (metal) buckets colliding with casing wall (due to
insufficient belt tension, defective belt, loose buckets) or with
discharge chute
• Misalignment of pulley
Electrical equipment • Electrical equipment and motors
• Inadequate earthing and/or equipotential bonding
Electrostatics • Electrostatic charging due to separation processes between belt and
drive pulleys
• Electrostatic charging of buckets due to electrostatic induction
• Electrostatic charging of any other non-earthed conductive
installation components
5.2.2.3 Ignition sources introduced or acting from outside
Bucket elevators being part of an installation configuration have interfaces which should also be taken
into account. This means that ignition sources that may be introduced into the bucket elevators should
be considered in addition to the equipment related ignition sources.
A summary of the typical potential ignition sources introduced or acting from outside is shown in
Table 2.
Table 2 — Potential ignition sources introduced or acting from outside
Potential ignition source Possible causes
Hot surfaces • Introduction of foreign material
• Introduction of glowing nests
• Welding, grinding, cutting operations
• Damage to the casing due to external mechanical action
Flames and hot gases • Introduction of glowing nests
including hot particles
• Propagation of fire or explosion from connected installations or from
outside
Mechanical sparks • Introduction of foreign material
• Damage to the casing due to external mechanical action
Lightning • Lightning protection inadequate
5.2.2.4 Ignition sources arising from the product itself
There are also ignition sources possible arising from the product itself. Therefore one should check
whether self-ignition or exothermal decomposition are to be expected due to the characteristics of the
bulk material.
Such exothermal reactions should be assumed to occur particularly in installations operating at
elevated temperatures and in which large coherent dust accumulations form either intentionally
(storage, intermediate storage, etc.) or unintentionally (deposits, cakings).
In the case of organic products (such as grain), an excessive moisture content may furthermore pose the
risk of self-ignition due to microbiological processes (Maillard reaction).
In bucket elevators, large product accumulations may occur in the boot and in horizontal infeed and
outfeed sections. It should be taken into account here that the self-ignition or degradation temperature,
which is characteristic of the self-heating behaviour of any dust, will decrease as the volume and layer
thickness increase. Glowing nests and smouldering fires having formed by self-ignition may become
ignition sources for dust explosions when deposits are whirled up.
Particularly with some organic bulk materials, there is the additional danger of smouldering before self-
ignition, which can release combustible gases such as carbon monoxide with wood (formation of hybrid
mixtures).
Self-ignition and exothermal decomposition require the dust heap to be exposed to elevated
temperatures for a sufficient time; the specific induction time, i.e. the time between the beginning of
storage and the ignition of a particular dust heap should be reached for this to occur.
NOTE If there is a suspect of burning material in the product upstream of the bucket elevator, the product
should be discharged into the open air and not through the bucket elevator.
5.2.3 Effect of ignition: smouldering product, fire, explosion, propagation of explosion
After ignition it will depend upon the presence of dust deposits or explosive clouds whether
smouldering product, fire or an explosion will occur. In most cases ignition arises in the head or the
boot (due to the high probability of ignition sources at these locations).
If smouldering products are formed they may be transported further into the downstream process (i.e.
a silo) and may become an additional hazard.
In the case of fire, apart from fire damage to the bucket elevator, there also may be damage due to
transport of burning product via the de-dusting system and the bucket elevator outlet, which may lead
to fire or explosion downstream.
In the case of an explosion, the dust explosion characteristics in combination with the bucket elevator
design (protection of bucket elevator, strength of bucket elevator) will determine the actual explosion
course. An explosion may propagate to connected equipment leading to secondary explosions and/or
fires. If the pressure exceeds the strength of the bucket elevator, failure of the casing will occur and
flame jets and fire balls are formed which may cause secondary explosions and/or fire especially in
dusty environments.
5.2.4 Risk assessment
The likelihood of explosive atmospheres, presence of ignition sources and actual ignition will determine
the likelihood of a fire or an explosion. The location of the bucket elevator and the presence of adequate
protective systems will determine the consequences of a fire or an explosion.
The need to take additional preventive and/or protective measures will strongly depend on the
situation: is ignition likely or not, can the effects be tolerated or not, are the risks acceptable or not?
The user normally selects a bucket elevator based upon the category (related to internal zone) and then
shall perform a risk assessment based upon the local circumstances. Such a risk analysis shall include
the probability that ignition sources enter from outside (see 6.3.2.2) but also the potential
consequences of an explosion. Depending upon the acceptability of risks, in addition to preventative
measures (based upon category of the bucket elevator) explosion protection measures may be needed.
5.3 Fire hazards
In addition to the explosion hazard addressed in this report, combustible products and combustible
construction materials inside bucket elevators (e.g. belt, buckets) can also present a fire hazard that has
to be considered.
The vertical orientation and enclosed construction are favourable factors in terms of fire spread and
unfavourable for controlling a fire. A fire developing in a bucket elevator, where combustible dust is
present, can lead to a dust explosion or flash fire. A dust explosion often results in an ensuing fire, even
when explosion mitigation techniques are used.
For assessing the fire hazard in bucket elevators, the combustion characteristics of the following must
be known: combustible materials used (such as the belts and buckets), of the material to be conveyed
and of the dust occurring primarily during transport. For assessing the dust, the combustion class (BZ),
the glowing temperature and the self-ignition characteristics of the dust can be used. Ignition sources
can be introduced from outside (such as glowing nests, hot particles) or may be generated inside the
bucket elevator (e.g. hot bearings, buckets scraping, return or drive pulley heating up due to slippage).
Furthermore, deposits of material conveyed must be checked for possible self-ignition processes or
exothermal degradations.
The combustion class BZ (see VDI 2263-1, an EN standard is in preparation) characterises the
combustion behaviour of deposited bulk material/dust and will at least allow a rough estimation as to
whether deposited dust will ignite or whether ignited dust will allow glowing combustion or flaming
combustion to develop. Furthermore, it must be noted that burning dust is to be considered an ignition
source in itself.
In the combustion classification an attempt is made to ignite a defined dust heap by a hot wire or flame.
The results will lead to classification of the dust into the following Combustion Classes:
— BZ 1 no ignition;
— BZ 2 brief ignition, rapid extinction;
— BZ 3 localised combustion or glowing;
— BZ 4 spreading of glowing combustion;
— BZ 5 spreading of flaming combustion;
— BZ 6 explosion-like combustion.
No fire protection measures are required as a matter of principle where non-combustible dusts or dusts
of combustion class BZ 1 are handled and provided that no other combustible materials (such as belts
and buckets including materials to be conveyed) are present.
With dusts of combustion classes BZ 2 or BZ 3 in the presence of non-combustible belts and buckets, or
dusts of combustion class BZ 1 in the presence of combustible equipment installed in the bucket
elevator, fire precautions are usually sufficient.
For combustion class BZ 4 a case by case evaluation of the fire protection and damage control measures
is recommended, based on the presence of combustible equipment in the bucket elevator and the speed
of propagation in the burning test.
For dusts of combustion class BZ 5, both fire precautions and measures for damage control in the event
of fire should be considered irrespective of the presence of any further combustible materials.
Due to the high mass burning rate, dusts with a combustion class BZ 6 call for an individual assessment,
which is not within the scope of this document.
6 Fire and explosion prevention and protection of bucket elevators
6.1 General
Fire and explosion protection is to be based upon the following basic measures:
— prevent deposits of combustible materials and explosive mixtures;
— prevent ignition sources.
If prevention is not sufficient additional measures shall be taken, such as fire fighting (extinguishing)
and/or explosion protection (explosion containment, explosion venting, explosion suppression in
combination with explosion isolating measures).
6.2 Fire prevention and protection
6.2.1 Fire prevention
The use of combustible construction materials will increase the fire hazard. From the fire hazard
perspective, bucket elevator components like the enclosure, the buckets and the belt should be non-
combustible and/or not supporting or propagating combustion. These are e.g. materials classified as A1,
A2 or B according to EN 13501-1 (see EN 13478).
When not in service, combustible products should not be stored in bucket elevators.
All ignition sources, that are controlled in order to prevent dust explosions, will also prevent fires.
Therefore, for ignition source control measures see 6.3.2.
6.2.2 Fire protection
Manual fire fighting
Manual firefighting by plant personnel should not be relied on to control and extinguish a bucket
elevator fire, unless the fire is detected in its early stages. Besides fire and explosion hazard for plant
personnel, smoke will develop, hindering firefighting efforts due to poor visibility. In particular, plastic
construction materials produce large amounts of toxic, black smoke when involved in a fire.
Automatic fire protection
Fire protection in a building by means of automatic sprinklers will not control a fire inside a bucket
elevator because ceiling sprinklers will not be activated and if sprinklers are activated, the inside of the
bucket elevator is shielded from sprinkler water. Fire protection by means of automatic sprinklers
inside the bucket elevator will ensure control of the fire to prevent fire spread inside the bucket
elevator and will limit the overall consequences of a fire.
If a risk assessment has shown that fire protection for bucket elevators is required, this can be done as
follows.
1) Provide automatic sprinkler protection at the top of the vertical bucket elevator leg where the
enclosure is non-combustible. If the enclosure is constructed from combustible materials, provide
additional automatic sprinkler protection along the leg (i.e. treat it as a vertical shaft with
combustible sides).
2) Design the automatic sprinklers to deliver a minimum end sprinkler pressure of 1 bar, using
sprinklers with a K factor of 115 (14 mm) or greater. Temperature rating of the sprinklers should
be 70 °C. Sprinklers with a temperature rating of 100 °C may be used in locations where the
ambient temperature is in excess of 43 °C. For locations prone to extremely cold and freezing
conditions, use dry-pipe sprinkler systems with a temperature rating of 140 °C.
3) Connect the automatic sprinkler system to an adequate and reliable water supply.
4) The bucket elevator driving mechanism should be interlocked to shut down automatically on
sprinkler water flow or fire detection if continuing operation could spread fire to other areas. This
is especially important when a bucket elevator is installed inside a building and runs through a fire
wall or floor (fire compartment) but also when different building floors are protected by means of
automatic sprinkler systems. This is because fire spread to other areas will overtax the sprinkler
system. Penetrations in fire rated walls and floors should be properly sealed or protected.
Manual shutdown is acceptable where all of the following are provided:
i) The area is constantly attended during conveyor operation or fire detection is provided.
ii) There are documented shutdown procedures for the conveyor system, and operators have been
trained in shutdown procedures.
iii) Controls are easily accessible in a fire situation involving the conveyor.
iv) Other protection is adequate.
v) For the design of the bucket elevator, take into account the mass of filled buckets and accumulation
of water in the bucket elevator. Drainage of water should be considered.
6.3 Explosion prevention and protection
6.3.1 Prevention of explosive atmospheres
When conveying combustible bulk materials with a fine-fraction grain size smaller than 500 μm,
potentially explosive atmospheres can occur inside bucket elevators. This holds, in particular, for very
fine bulk materials and bulk materials with a high dust content.
Explosive dust and explosive atmospheres can be expected to accumulate particularly at charging,
transfer and discharging stations. The avoidance of explosive atmospheres cannot, therefore, be the
sole precaution in most cases.
By taking appropriate measures, however, it is nevertheless possible to reduce the likelihood of
occurrence, and the extent of the explosive atmosphere inside the bucket elevator. Such appropriate
measures can include:
— dust removal systems at charging, transfer and discharging stations where the material to be
conveyed has a low dust content;
— conveying speeds as low as practical;
— avoidance of surfaces where deposits can form;
— avoidance of material conveyed being returned;
— removal of dust deposits by means of appropriate discharge systems;
— binding of dust using, e.g. water, oils (high boiling point, no volatile constituents);
— periodic cleaning.
Regarding the environment of the bucket elevator, in many cases, dust is released into the area around
the bucket elevator due to leaks, particularly at charging, transfer and discharging stations as well as
openings (inspection doors) of the bucket elevator. This may result in considerable dust deposits,
particularly in the release areas, but also on external surfaces. The extension of dust deposits can be
reduced by periodic cleaning.
Summarising, prevention of explosive atmospheres inside bucket elevators is not really feasible when
dealing with dusty products or with products containing dust. Dedusting systems can reduce the dust
concentration locally but are unlikely to prevent explosive atmospheres throughout the bucket elevator.
Inerting is one option for preventing the formation of an explosive atmosphere inside the bucket
elevator.
6.3.2 Prevention of ignition sources
6.3.2.1 Equipment related ignition sources
The equipment related ignition sources are listed in Table 1.
If these ignition sources are to be considered effective ignition sources on account of the characteristics
of the material to be conveyed (e.g. minimum ignition energy, minimum ignition temperatures), they
will have to be assessed in terms of their likelihood of occurrence.
The manufacturer of a bucket elevator to be used for conveying flammable products shall carry out an
ignition hazard assessment and based upon this analysis will indicate in which category the internal
part of the bucket elevator will fall. The manufacturer puts this bucket elevator on the market with this
category indication and the limits of use in relation to the products involved and equipment parameters
(speed, temperature etc.). An example of such an analysis (according to EN 13463-1) is given in
Annex D.
The likelihood of occurrence of potential ignition sources can be reduced by technical measures, such as
selection of appropriate bearings and appropriate materials, and by organisational measures (e.g.
maintenance).
To reduce the likelihood of these ignition sources occurring, measures to control ignition sources may
also be required, e.g. misalignment, slip monitors and temperature detection on bearings.
With slip monitoring, the speed of the return pulley is compared with the drive pulley in order to detect
belt slippage. The aim is to prevent overheating due to friction.
NOTE 1 during start-up initially there will be some friction, which needs to be taken into account in the design
of the slip monitoring, for example an alarm delay of maximum 10 s during start-up.
The misalignment monitor checks the lateral movement of the belt towards the casing, preventing the
generation of hot surfaces and of sparks due to friction between buckets, belt and casing.
NOTE 2 If the bucket elevator is intended for use in a potentially explosive atmosphere, it is also the
responsibility of the manufacturer to prevent the bucket elevator from creating an ignition source in the
surrounding atmosphere. In that situation, apart from an internal ignition source analysis, an external ignition
hazard analysis is also required.
Table 3 shows the recommendations for all bucket elevators that will transport explosive dusty
products.
Table 3 — Recommendations for all bucket elevators
No Requirement Information
1 General All bucket elevators within the scope of this document should
comply with the requirements contained in EN 13463–1 unless
stated otherwise in this document.
2 Ignition hazard assessment Normal operating conditions: Normal operating conditions
should be considered to occur in situations where the bucket
elevator performs its intended use within its design
parameters. This includes conditions during start up and shut
down. (See also EN ISO 12100.)
For the purposes of bucket elevators made according to this
document, failures (such as a breakdown of bearings, slip,
misalignment or releases of substances caused by accidents)
which involve repair or shut-down are not considered to be
part of normal operation.
No Requirement Information
Expected malfunction: An expected malfunction should be
considered to be a failure or a fault in a bucket elevator that
normally occurs in practice.
In addition, an expected malfunction should be considered to
occur when a bucket elevator or its components do not perform
their intended functions.
For the purposes of bucket elevators made according to this
document this can happen for a variety of reasons, including:
• Malfunction of bearing and/or seal
• Slip of belt on pulley due to overload, stray object causing
obstruction, belt tension problems, belt/pulley wear, too
warm product or environment leading to belt elongation
etc.
• Misalignment of belt due to overload etc.
• Misalignment of pulley due to bearing malfunction or
failure of pulley/shaft connection.
• Loss of buckets or fixation elements due to wear or
vibration leading to obstruction of belt and pulley.
• Loss of pulley friction elements due to wear or vibration
leading to obstruction of belt and pulley
• Choking of bucket elevator
Rare malfunction: A rare malfunction is a type of malfunction
which is known to happen but only in rare instances. An
example of a rare malfunction is sudden breakage of a belt or
chain. Two independent expected malfunctions which,
separately, would not create an ignition hazard but which, in
combination, do create an ignition hazard, are regarded as a
single rare malfunction. As an example, misalignment of belt
with failure of misalignment detector.
3 Assignment to equipment Depending on the outcome of the ignition hazard assessment
categories the manufacturer can indicate the internal and external
category of the bucket elevator.
4 Temperature limits These are the temperatures of the environment in which the
bucket elevator can be located and the admissible temperatures
of the product being conveyed.
5 Mechanical design criteria The strength of the bucket elevator in relation to internal over-
pressure should be given but also wall thickness and
construction details in relation to stability of the bucket
elevator and to wear and corrosion. Preferably the casing
should to be manufactured from non-combustible material.
6 Speed Typically 1 to 4 m/s, keep as low as practical.
7 Material combinations Prevent combinations of light metal and carbon steel.
No Requirement Information
8 Pulleys Crowned drive and return pulley design and if cover is required
then use antistatic flame retardant material.
If pulley is assembled out of several parts then measures should
be taken to ensure integrity is maintained.
9 Belt and chain: material and Use dissipative material (surface resistance on both
construction. sides < 3 × ˜10 Ohm™, according to IEC/TS 6
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