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

Status
Published
Publication Date
23-Apr-2019
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
24-Apr-2019
Completion Date
24-Apr-2019

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SLOVENSKI STANDARD
SIST-TP CEN/TR 16829:2017+AC:2019
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
SIST-TP CEN/TR 16829:2017+AC:2019 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST-TP CEN/TR 16829:2017+AC:2019
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SIST-TP CEN/TR 16829:2017+AC:2019
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.
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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

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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

˜ ™.
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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)
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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
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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.
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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

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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
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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,

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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.
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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 degradatio
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