The implications of the ATEX Directives onConveyors and Big Bag Handling Systems

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CONVEYING & BIG BAG HANDLING SOLUTIONS

Zone 20: A place in which an explosive atmosphere in the form of a cloud of combustible dust is presentcontinuously, or for long periods or frequently.

Zone 21: A place in which an explosive atmosphere in the form of a cloud of combustible dust is likely to occurin normal operation occasionally.

Zone 22: A place in which an explosive atmosphere in the form of a cloud of combustible dust is not likely tooccur in normal operation, but if it does occur will persist for a short period only.

ATEX Directive 1999/92/E on minimum requirements for improving the safety and health protection ofworkers potentially at risk from explosive atmospheres came into European Law in January 2000. Inthe UK, the ATEX Directive has been implemented by the Dangerous Substances and ExplosiveAtmospheres Regulations 2002 (DSEAR). The Directive requires that the specific risks arising fromexplosive atmospheres be assessed. As part of the control of explosion risks, the Directive also requiresthat employers classify places where explosive atmospheres may arise and select appropriate workequipment for use in these areas.

Spiroflow Flexible Screw ConveyorThe basis of safety for all Spiroflow equipment is explosionprevention. This requires all the equipment parts to be earthbonded to one common earth point. The customer should ensurethat no foreign object can enter the system.

Insufficient temperature increase to create a risk.No friction heat build-up takes place as the tubematerial has a low coefficient of friction and allowsthe spiral to rotate and slide easily. Cleaning andgood housekeeping by customer to avoid dustlayer build-up.

Potentialignitionsources

Surfacetemperature of thehousings,conveying tubesand moving parts

The conveyors are manufactured from carbon steelor stainless steel. No parts of the equipment usesaluminium parts with a magnesium content ofmore than 7.5%.

Materials ofconstruction (lightmetals)

Spiral failure is only considered to be arare malfunction and therefore need notbe considered for Zone 22 or Zone 21.The user instruction manual details thecorrect set-up procedure to prevent thisproblem.

Spiral failure

The ingress of foreign objects into the conveyor viathe customer’s feed or by operator intervention,can cause (if the size is large enough) theconveyor to jam or the spiral to fail. Precautionsmust be taken by the user to avoid this.

The gearbox anddrive motors areselected andobtained from thesupplier to meet theZone requirement.

Foreign objects inpowder

Gearbox anddrive motor

The spiral is earthed and willdischarge the powder as itflows. Some residual chargemay be carried on to the rest ofthe process beyond themachine from the outlet.Equipment should be earthed.

Static discharge at theoutlet of the conveyor

The external surface of thetube does not have a chargingmechanism in normaloperation. Anti-static tubes areavailable for gaseousenvironments.

Static discharge on theoutside of the conveyortube

Flammable dust concentrations are not normally presentinside the tube and the inside of the conveying tube isconsidered a Zone 22 area. The spiral is earthedthrough the gear box/motor drive which ensures theenergy from any static discharges are limited to lessthan 3 milli-Joules. Anti-static tubes are available foruse with materials sensitive to such low energydischarges.

Static charge onthe inside of theconveyor tube

A level switch is to be fitted at the inlet of theconveyor to prevent it running empty.

Running empty

Correct setting of the infeed restrictor preventsoverload occurring.The receiving equipment at the outlet must befitted with a High-Level switch.

Conveyor overloading

Control measures

Spiroflow Aero-Mechanical ConveyorThe basis of safety for all Spiroflow equipment is explosion prevention. This requires all the equipment parts to beearth bonded to one common earth point. The customer should ensure that no foreign object can enter the system.

The selection of equipment both electrical and mechanical for use in hazardous areas should be based on thecategories specified in the ATEX/DSEAR regulations as follows, unless the risk assessment finds otherwise:

Zone 20: Category 1D equipment

Zone 21: Category 1D or 2D equipment

Zone 22: Category 1D, 2D or 3D equipment

Static discharge at theoutlet of the conveyor

Materials of construction (lightmetals)

Rope failure

The gearbox and drivemotors are selectedand obtained from thesupplier to meet theZone requirement.

Gearbox and drivemotor

Static discharge on the outside ofthe conveyor tube

Static charge on the inside of theconveyor tube

The conveyor is earthed and will dischargethe powder as it flows. Some residualcharge may be carried on to the rest of theprocess beyond the machine from the outlet.Equipment should be earthed.

The conveyors are manufactured fromcarbon steel or stainless steel. No parts ofthe equipment uses aluminium parts with amagnesium content of more than 7.5%.

Foreign objects inpowderThe ingress of foreignobjects into the conveyorvia the customer’s feedor by operatorintervention, can cause(if the size is largeenough) the conveyor tojam or the rope to fail.Precautions must betaken by the user toavoid this.

Surface temperature of the housings,conveying tubes and moving partsInsufficient temperature increase to create a risk. Nofriction heat build-up takes place as the discmaterial has a low coefficient of friction and allowsthem to slide easily.Good levels of clearance between the discs and thetube also minimise the risk.Cleaning and good housekeeping by customer toavoid dust layer build-up on external surfaces.

Rope failure is only considered to be a rare malfunctionand therefore need not be considered for Zone 22 orZone 21.The user instruction manual details the correct set-up andmaintentenance procedures to prevent this problem.

The external surface of the tube does nothave a charging mechanism in normaloperation.

The conveyor is earthed through the gearbox/motor drive and this ensures frequentincendiary discharge does not occur. Conveyor

overloadingCorrect setting of theinfeed valve preventsoverload occurring.The receivingequipment at the outletmust be fitted with aHigh-Level switch.

Spiroflow Big Bag (FIBC) FillersThe basis of safety for all Spiroflow equipment is explosion prevention. This requires all theequipment parts to be earth bonded to one common earth point. The customer should ensure thatno foreign object can enter the system.

Intended usage of the equipmentSpiroflow manufactures equipment in the line with Manufacturers Directive 94/9/EC. Our conveyorsand bulk bag handling equipment are intended for transporting/handling powders and/or granularmaterial, either inside or outside a building containing a potentially explosive atmosphere and theyare constructed to meet the requirements of Group II, Category 3 equipment.

Static discharge from the filleritselfAll filler parts are fastened together and areprovided with an earth point.

No frictional heating orsparking can occur dueto the slow speedsinvolved.

Surface temperature of the fillerInsufficient temperature increase tocreate a risk.Cleaning and good housekeepingby customer to avoid dust layerbuild-up.

Load cells, vibration,level switches andother electricalequipmentAll electrical equipmentis selected and obtainedfrom the supplier tomeet the Zonerequirement.

Impact due to off-loading of the bigbag (FIBC) afterfillingWhere a fork lift truck isbeing used, it isrecommended that itsspeed be kept to below1 metre / second.

Static discharge fromthe big bag (FIBC)The big bag (FIBC) isnot part of Spiroflow’ssupply.Further information onstatic dissipative or staticconductive bags shouldbe obtained from theFIBC supplier. Spiroflowcan supply staticgrounding andmonitoring devices.

Materials of constructionThe fillers are manufactured fromcarbon steel or stainless steel. No partsof the equipment uses aluminium partswith a magnesium content of morethan 7.5%.

Pneumatic controland operationsequence

Heat friction orsparking due tomoving parts

The pneumatic controlpanel and componentsare selected to meet theZone requirement.

Spiroflow Big Bag (FIBC) DischargersThe basis of safety for all Spiroflow equipment is explosion prevention. This requires all theequipment parts to be earth bonded to one common earth point. The customer shouldensure that no foreign object can enter the system.

The risk factors mentioned in this leaflet are intended as a guideline only and donot attempt to represent an exhaustive list of all possible risks. Spiroflowequipment varies depending upon the customer’s application and the equipmentspecified. Individual risks associated with each application must be assessed foreach installation.

The speed of integral hoist is too slow to cause anysparks.Where a fork lift truck is used, the lowering speedmust be kept to below 1 metre / second.

Impact due to loadingof the lifting frame ontothe upper support frame

All discharger parts are fastenedtogether and are provided with an earthpoint.

Static discharge from thedischarger itself

All electrical equipment isselected and obtained from thesupplier to meet the Zonerequirement.

Safety interlock switchesand level probes

No frictional heating orsparking can occur due to theslow speeds involved.

Heat friction or sparkingdue to moving parts

The pneumatic control paneland components are selectedto meet the Zone requirement.

Pneumatic control andoperation sequence

The dischargers are manufactured from carbonsteel or stainless steel. No parts of theequipment uses aluminium parts with amagnesium content of more than 7.5%.

Materials of construction

The hoist isselected andobtained from thesupplier to meetthe Zonerequirement.

Integral hoist

Insufficient temperature increase to create a risk.Cleaning and good housekeeping by customerto avoid dust layer build-up.

Surface temperature of the discharger

The big bag (FIBC) isnot part ofSpiroflow’s supply.Further informationon static dissipativeor static conductivebags should beobtained from theFIBC supplier.Spiroflow can supplystatic grounding andmonitoring devices.

Static dischargefrom the bigbag (FIBC)

Static dischargefrom the plasticwindow need notbe considered fordusts with aminimum ignitionlevel of >3mJ.

Static dischargefrom the plasticviewing window

• Quaker Oats• Walkers Snack Foods• FMC Biopolymer• Colin Stewart Minchem• Bayer Crop Science• A J Barber (Barbery)• Ceraform• United Trent Water• United Biscuits• William Grant & Sons Distillers• Tetley GB

• Novartis• Proctor and Gamble• Dow Chemical• Kellogg Co Great Britain• Rieber and Sons• Saudi Formaldehyde• Process & Vessel• Carlisle Process• Russell Finex• Laurens Patisserie

Some of the numerous customers for whom we have supplied ATEX rated equipment

At Spiroflow we are familiar with the following elements

• Secondary explosion types• Control of dust in the work area• Dust explosion prevention and protection• Thermal decomposition properties• Fire and combustion properties

• Dust cloud characteristics• Minimum ignition energy• Dust explosion classification• External ignition sources• Internal ignition sources

Although ultimately the responsibility is yours to ensure that your factory/workingenvironment is safe, we can guide you through the ATEX maze and help ensure thatyour ‘Spiroflow’ Conveyors and Big Bag Handling Equipment are not over-specifiedand therefore not more costly than they need to be.

As we are specialists in powder handling, in this leaflet we have largely concentratedon the hazards associated with finely divided materials. However, our equipmentoften has to work in environments in which there are hazardous gases and we fullyunderstand those risks too.

We work closely with Phoenix Loss Prevention Ltd of Skipton, North Yorks and wewould not hesitate to put you in touch with them for professional and independentadvice on all aspects of the ATEX/DSEAR regulations and how they apply to yoursituation.

Spiroflow Limited

Lincoln Way, Clitheroe, Lancashire BB7 1QG, UK

Tel: +44 (0)1200 422525 Fax: +44 (0)1200 429165

E-mail: sales@spiroflow.comWebsite: www.spiroflow.com

CONVEYING & BIG BAG HANDLING SOLUTIONS