“Fire in the hole!"
Once a common phrase heard throughout mines, the words warn that a dynamite charge has been set and an explosion is imminent. Dynamite...Gunpowder... TNT. We all associate these terms with explosions, detonations and fire. But did you know that gunpowder is actually classed as a low explosive powder? In fact, in high concentrations, common household flour is several times more dangerous than gunpowder. And sugar dust is four times more powerful, weight-for-weight, than TNT.
The seemingly sweetly innocent cocoa powder is equally dangerous. In March 2023, a bustling Pennsylvania chocolate factory suffered a gas leak. The leaked gas was enough to ignite the powder-laden atmosphere, causing the cocoa powder and corn starch to detonate in milliseconds. The blast ripped through the factory at a speed faster than sound, destroying several buildings and ultimately claiming seven lives.
This tragic example is just one of many devastating explosions that occur worldwide at facilities where dusts are present. The constant risk of a deflagration has led regulators to draw up a series of standards for explosion protection, such as NFPA 660 (incorporating NFPA 652) and NFPA 68. These are aimed at ensuring safer working environments at any manufacturing or processing plant that handles combustible dusts.
Active explosion suppression systems
These detect and automatically (actively) extinguish explosions as soon as they begin, often within milliseconds. Sensors detect a rapid rise in heat and/or pressure and send a signal to the control panel. This triggers the suppression mechanism, which releases a suppressing agent (a dry powder, liquid nitrogen, water or other specialist chemical) into the explosion zone. This ends combustion, reduces flame propagation, and lowers pressure, preventing the explosion from spreading any further.
Passive explosion relief technology
Explosion relief panels
Explosion relief panels prevent catastrophic damage from explosions and deflagrations by opening at a set pressure before other parts of the system begin to fail. Fire, heat, and pressure are vented into a safe area outside the building or vessel.
Flameless vents
Flameless vents present a compact alternative to panels and ductwork. They combine an explosion panel with a stainless steel mesh. During deflagration venting, the panel bursts, allowing pressure, heat, gas, and particles to safely exit the vessel or pipework. The mesh quenches the flame and cools the burning dust or gases to below their ignition temperature. Fire and dust are retained within the flameless vent body. All that emerges is smoke.
Example: Xplo-Gard, an innovation in flameless venting
Xplo-Gard is an innovative flameless venting solution for enhanced explosion and deflagration protection. The vent is easy to install and maintain, with an access hatch that allows you to easily install an explosion panel inside the vent body after attaching the vent body to the vessel or ductwork. The panel is protected during installation, and is easy to install after attaching the vent body to the vessel or ducting. An inspection window on the light-weight models allows you to easily check dust levels and panel status without depressurizing the system. We also offer Xplo-Gard with an optional curved flange for installation directly onto cylindrical vessels to minimize dust build-up.
Explosion isolation
Explosion isolation valves prevent explosions from spreading upstream from a dust collector or other vessel. A flap in the valve closes as the pressure wave from the explosion hits it, preventing further travel upstream, and protecting workers, equipment, and the facility.
Prevent dust explosions
“Prevention is better than cure”. Deflagrations and explosions are often caused by nothing more than a simple accumulation of dust. This could be avoided by taking preventive measures such as:
- Maintaining adequate ventilation throughout the facility to prevent dust collecting orreaching dangerous concentrations.
- Good equipment maintenance to ensure machinery and systems do not exceed allowable temperatures and pressures.
- Good housekeeping, including routine inspection and cleaning of places prone to dust accumulation. The NFPA provides guidance on proper cleaning methods and protections.
- Preventing or minimizing the escape of dust, especially by addressing fugitive dust emissions and leaks.
- Conducting regular inspections, measurements, evaluations and risk assessments. Be familiar with OSHA and NFPA standards that provide guidance on excessive dust loading. Use safety data sheets, explosibility and combustibility analyses, and other relevant data to assess potential risks.
All of these active and passive dust explosion protection systems may be used individually or in combination to protect equipment in the powder and bulk handling industries. These range from food and beverage, wood, paper, pulp, paints and pigments to chemical processing and pharmaceutical manufacturing.
Whatever your facility, if dust is present, it is crucial to determine whether the dust is considered combustible, and if your application requires deflagration venting. We recommend you test your dust to find its KSt value, and refer to applicable dust explosion and combustible dust standards to ensure you have appropriate safety measures in your facility.