DUST EXPLOSION PROTECTION IN FEED MILLS ACCORDING TO THE EUROPEAN ATEX DIRECTIVES –

1. Forschungsinstitut Futtermitteltechnik Research Institute of Feed Technology DUST EXPLOSION PROTECTION IN FEED MILLS ACCORDING TO THE EUROPEAN ATEX DIRECTIVES – RISK ASSESSMENT AND NEW FINDINGS Dipl.-Ing. Alexandra Kirchner IFF-Forschungsinstitut Futtermitteltechnik Braunschweig-Thune

2. Cases of damage Film

3. Pre-conditions of a dust explosion high degree of dispersion of flammable substances dust explosion concentration of the flammable substances in air within their combined explosions limits effective ignition source

4. Statistics Dust explosions of food and feed powder, damaged equipment: • conveyor 27.1 % • mills 22.9 % • silos 21.4 % • dryer 8.6 % • combustion plants 2.9 % • sieves 2.9 % • dust-extractions systems 2.9 % • other 11.4 % reference: BG Nahrungsmittel und Gaststätten

5. Regulation standards for producers of equipment standards for plant operator European regulation ATEX 100 a (95) 94/9/EC ATEX 137 1999/92/EC national regulation equipment safety worker protection

6. Assessment of explosion risks • Assessment of explosion risks focuses on • The likelihood that an explosive atmosphere will occur • The likelihood that ignition sources will be present and become effective

7. Classifaction of hazardous areas (1999/92/EC) • Zone 20 a place in which an explosive atmosphere in form of a cloud of combustible dust in air is present continuously, or for long periods • Zone 21 a place in which an explosive atmosphere in form of a cloud of combustible dust in air is likely to occur in normal operation occasionally • Zone 22 a place in which an explosive atmosphere in form of a cloud of combustible dust in air is not likely to occur in normal operation but, if it does occur, will persist for a short period only

8. Zoned areas of hazard – examples for a feed mill raw material silos premixsilos sieves mills conditioner fat expander pellet mill scale cooler fat, molasses, etc. main mixer roller mill Zone 20 Zone 21 continuous mixer Zone 22 no Zone

9. Requirements for equipment in hazardous areas (94/9/EC) • In accordance with the three zones, three device categories are defined which are subdivided according to the relevant ignition-source reliability or absence: • Category 1: Ignition sources are avoided by two independent protection measures or safety despite two independent errors also at rare breakdowns • Category 2: Ignition sources are avoided in the normal operation and at frequent breakdowns • Category 3: Anticipated ignition sources are avoided in the normal operation.

10. Assessement of hazardous areas – state of knowledge • The dust concentrations in the interior of the plant components and in their surrounding, the frequency of explosive dust-air atmosphere and their changing in concentration over the duration are not always known • The current state of knowledge is mainly based on estimations so far • The results are uncertainties in the risk assessment as well as necessary safety equipment • State-of-the-art of science and technology is that knowledge on the dusting tendency can be taken as reference for an improved risk assessment concerning dust explosions

11. Selection of open questions • Coherence between dusting behaviour and the occurrence of explosive atmospheres? • Possibilities of predicting the occurrence of explosive concentrations of diffuse dusts on basis of the dust-formation behaviour? • Do diffuse dusts occur in the explosive concentration range at the reception area of raw materials? • ....

12. Designation of the dusting behaviour on the laboratorial scale • The requirements basically to be placed on a procedure for characterising the dusting behaviour of bulk materials result from the processes during which dust is set free and dispersed • For the processing of agro raw materials, this are mainly impact and shear stresses due to conveying and transporting

13. Test methods used sample funnel dust valve downpipe dust reservoir laser beam receiver control unit schematic drawing DustView Single-drop method Palas DustView Rotation-drum method Stauber-Heubach (standard)

14. Findings on the dusting behaviour – classification of all results class frequency dust indexes Worst case? Very strong dust release? class limits Strong dust release and significantly increased risk respectively? Increased dust release and increased risk respectively? Low to moderate dust release and risk respectively? frequency distribution dust indexes SF dust indexes SR http://www.iff-braunschweig.de/staubdb.de

15. Concentration determination of diffuse dusts – schematic build-up

16. Dimensions of bulk chute and build-up of measuring dropping rolling gate camera side-dump truck side-dump truck material flow 4200 1500 bulk chute reflection wall 5000 grid

17. Measurements at work – concentration profiles during the dropping process bulk chute without aspiration, with dust blockers pre-cleaned wheat moisture: 12.4 % SF: 2.06, SR: 1.11

18. Research findings • The measured results show that explosive dust concentrations can occur in the area above the grid at intervals of up to approx. 1.5 m • The present risk assessment when handling cleaned and pre-cleaned grain respectively as well as recommendations for the classification to zones in reception area for raw materials have to be revised

19. Research findings (2) • The evaluation of the measured results by means of the dust indexes shows for the considered application that this is alone not sufficient for assessing the frequency of the occurrence of explosive atmosphere • Besides machine and process parameters • amounts of bulk materials • dropping height and • the involved dispersion effect by displaced air masses have to be considered