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Step 5 – Part 3 – Own Source of Ignition

Dust Explosion Blogs

Dust Explosions – Not my problem. Are your sure?

Overview

• Are any of the powders used combustible?
• Literature data is useful for a first pass but combustibility data is highly dependent on particle size and moisture content.
• Lab testing of actual powder being used is required to give reliable design data.

Blogs

Part 1 – No Explosion Properties on the MSDS – Ergo the Dust is not Explosive

Overview

• Can the combustible dust(s) be replaced by non-combustible materials?
• If not, then consider reducing the inventory of the fuel to minimise the risk. 
• If the inventory is very small a hazardous zone of negligible extent could be created which is equivalent to a safe area.

Overview

Consider possible dispersion mechanisms:

• Pneumatic conveying;
• Milling;
• Fluid bed drying;
• Mixing and blending;
• Powder leaks and spillage.

Overview

• Carry out Hazardous Area Classification using EN 60079-10-2 or similar and define the location and size of any Zones 20, 21, and 22.
• Draft the drawings showing a plan and elevation of the hazardous zones.

Blogs

Part 1 – Blanket Ex Zones. An unnecessary evil?

Overview

Minimise the sources of ignition by carrying out an ignition hazard assessment using the methodology in BS EN ISO 80079-36

Blogs

• Part 1 – Overview
• Part 2 – Sources of Ignition and Minimum Ignition Energy
• Part 3 – Own Source of Ignition

Overview

• Is the explosion unconfined, partially confined/congested or fully contained?
• Assess the impact of pressure piling, material inventory and material properties.
• Consider location and potential injuries.

Overview

Simple measures include:

• good housekeeping;
• reduce inventory;
• eliminate/reduce dispersions;
• provide segregation; 
• change location.

Overview

• Assess whether the residual risk after all the protection measures implemented thus far is acceptable. Consider the overall risk of an ignition and likely consequences of an explosion.
• Zone 20 – High explosion consequences = unacceptable residual risk 
• Zone 22 – High explosion consequences plus high risk of an ignition source being present = unacceptable residual risk.

Overview

• Inert gas blanketing is frequently possible for enclosed equipment but not possible for hazardous zones outside equipment.
• Remember that inert gases are also asphyxiants.

Overview

If the residual risk is unacceptable and the oxidant can be excluded, then use this system to prevent an explosion occurring.

Overview

If the residual risk is unacceptable and the oxidant cannot be excluded, then use some form of mitigation such as explosion relief, explosion suppression, or explosion pressure resistant equipment.