Combustible Dusts A Design Guide

1. Combustible Dusts � A Design Guide 2008 Australasian Milling Conference

2. Agenda Why me? Design Guide Project Regulatory Responsibility AS4360 approach to managing risk Summary of Key Control Measures

3. Why me? RiskTech Pty Ltd Independent risk management consultancy Clients include: Weston Milling Inghams Manildra Group Ridley Peter McGee BE (Env) Masters (FSE) Specialise in asset protection Focus on insurable risk

4. Design Guide Project Inghams, Ridley, Weston Milling Confusion regarding selection of electrical apparatus Scope: Design considerations for managing combustible dusts Not limited to selection of electrical apparatus Focused on a new mill, but can also equally be applied to an upgrade Also provides ability to audit against for non-conformances

5. Design Guide Project Minimum Requirements Driven primarily by regulation Also includes common sense / easy to achieve controls such as maintenance and management controls e.g. housekeeping, no smoking rules and hot work permits. Best Practice requirements Driven primarily by insurance industry guides (FM Data Sheets, NFPA standards)

6. Regulatory Responsibility Key requirement: Electricity Acts ? AS3000 (Wiring Rules) ? appropriate electrical apparatus in hazardous areas ? relevant hazardous area standards (pre-curser to AS61241)

7. Regulatory Responsibility Also OH&S Acts and Duty of Care to provide safe workplace Only prescribed requirement in managing combustible dusts relates to electrical equipment

8. Hazardous Areas Standards revised/updated Major change � separation between combustible dusts and flammable vapours Complete new set of standards relating to combustible dusts � AS61241 series

9. AS61241 Key changes: Zoning: 20, 21, 22 Dust Layers Provides fire load; Provides source for secondary explosion

11. Electrical Apparatus Primary device Ex tD Also known as IP6X � similar to DIP. Other devices include Ex mD, Ex pD, Ex iD. NB: similar equipment in zone 20, 21, 22.

12. Selection of Electrical Apparatus � abridged version Where: Dust Layers < 7.5mm Max surface temp of equip 75�C < minimum dust layer ignition temp Then: Install IP6X, or IP5X for non-conductive dusts IP 5X & 6X

13. Combustible Dusts � The Hazard Explosion can occur when: Combustible dust present; Suspended in atmosphere in correct proportions with air (O2); and Ignition source is introduced

14. AS4360 Approach Risk = Likelihood x Consequence Reduce Likelihood: Avoid explosive atmosphere � i.e. avoid dust Avoid ignition sources Reduce Consequence: Control consequences � i.e. manage explosion

15. Design Guide � Key Controls Plant Layout and Building Materials Ignition Source Controls Electrical apparatus (already addressed) Dust control Explosion Control Specific equipment Management controls and maintenance

16. 1. Plant Layout and Building Materials Limit the size of zones Prevent dust accumulation Exclude services (e.g. steam) from zoned areas Limit access to zoned areas Egress Non-combustible building materials

17. 2. Ignition Source Controls Hot work - more strict controls in zoned areas Static � maintenance continuity testing Mechanical friction � prevent product accumulation at bearings Foreign materials � cleaning equipment Thermal decomposition Process heat � failsafe thermostat controls Hot surfaces � all surfaces < 100�C

18. 4. Dust control Reduce dust in suspension below the lower explosive limit (anywhere from 50-500g/m3) Design is crucial: Volume � sufficient to extract dust at pick up point; Velocity � avoid deposits in ductwork Air to cloth ration � consideration for maintenance Safety factor Extract at every point of change in product flow Redesign when changes are made

19. 5. Explosion control Explosion venting should be primary method. Vent externally; Ensure no structures/equipment exposed Suppression, containment, isolation, inerting other alternatives

20. 6. Specific Equipment e.g. Bucket Elevators Under-speed detection Track control Explosion venting Grinding Magnetic separation Air/gravity separation Monitoring for temperature and flow of air and grain

21. 7. Management Controls Housekeeping Maintain dust layers <5mm at all times Best Practice � audit program measuring layer thickness Management of change Training Maintenance Static earthing e.g. painting over explosion vents

22. Summary Only regulatory requirement relates to selection of electrical apparatus Electrical apparatus are only one of a number of design issues to be considered when controlling combustible dusts Design changes provide the opportunity to consider these issues

23. Lets help avoid this!