What is a Dust Explosion – Explosion Protection FAQs

Combustible dust explosion protection is a frequently misunderstood topic. Below, we’ve organized and defined much of the terminology found within the explosion protection industry.

General Explosion Protection Questions

What is Combustion?

A chemical process of oxidation that occurs at a rate fast enough to produce heat and usually light in the form of either a glow of flame (NFPA 68, 2018).

What is an Explosion?

The bursting or rupture of an enclosure or a container due to the development of internal pressure from a deflagration (NFPA 68, 2018).

What is Combustible Dust?

A finely divided combustible particulate solid that presents a flash-fire hazard or explosion hazard when suspended in air or the process-specific oxidizing medium over a range of concentrations (NFPA 654, 2017).

What is a Combustible Dust Explosion?

Rapid combustion of dust suspended in the air in a confined space.

Active vs Passive Explosion Protection Questions

What are Active Explosion Protection Solutions?

An active explosion protection system mitigates or prevents the effects of a deflagration using a pressure and/or infrared detector to notify a control panel to activate the respective explosion protection devices. Active explosion protection solutions include:

What is an EPC (Explosion Protection Controller)?

Continuously monitors the protected hazard, reacts to incipient explosions and instantaneously actuates the explosion protection system (suppression and/or valves). Can act as a standalone controller or interfaced with other EPC’s for larger system. Explore Fike’s detection and control systems.

What is Explosion Suppression?

The technique of detecting and arresting combustion in a confined space while the combustion is still in its incipient stage. Explosion suppression prevents the development of pressures that could result in an explosion.

  • Suppression Agent – The chemical agent used in a deflagration suppression system to extinguish the deflagration (NFPA 69, 2014). Fike primarily uses Sodium Bicarbonate and Dessikarb (Food Grade Sodium Bicarbonate).
  • Chemical Isolation – A means of preventing flame front and ignition from being conveyed past a predetermined point by injection of a chemical suppressant.
  • HRD (High Rate Discharge Container) – Suppressant container used to suppress equipment at the onset of a deflagration for both suppression and isolation.
  • SRD (Standard Rate Discharge) – Suppressant container (9 liter) used specifically for chemical isolation.
  • Inert Gas – A gas that is noncombustible and nonreactive. Fike HRD and SRD are filled with inert gas nitrogen.

What are Active Explosion Valves?

Designed to close within milliseconds of the EPC detecting a deflagration to prevent flame propagation into connected pipes and equipment.

  • Explosion Isolation Valve (EIV, FAV) – Mechanical device in which a high-speed slide gate is shut upon activation to prevent spark, flame or pressure propagation beyond the valve. Learn more about Fike’s Explosion Isolation Valve (EIV).
  • Explosion Isolation Pinch Valve (EIPV) – Mechanical device in which an elastomer sleeve is pinched shut to full closure at high speed upon activation to prevent spark, flame or pressure propagation beyond the valve. Learn more about Fike’s Explosion Isolation Pinch Valve (EIPV).

What are Burst Indicators?

A device used to notify the system that the explosion vent has opened. May be used to activate alarms, bells or remote annunciators, and may be interfaced with process control systems to support safety follow-up initiatives.

What are Passive Explosion Protection Solutions?

A passive explosion protection system mitigates or prevents the effects of a deflagration in which the explosion protection devices are activated in response to the deflagration pressure.

What are Passive Explosion Valves?

Designed to close within milliseconds from the explosion pressure itself to prevent flame propagation into connected pipes and equipment.

  • Flow-Actuated Flap Valve – Air flow opens the flap to allow normal process conveyance conditions. However, when an explosion occurs in an adjacent vessel, the flow will reverse, causing the flap to close onto its field replaceable seal, stopping explosion pressure and flame propagation. Learn more about Fike’s Flow-Actuated Flap Valve—ValvEx®.
  • Flow-Actuated Float Valve – Passive isolation device that uses a “floating poppet” attached to the valve stem. The flow of an explosion pressure wave drives the floating  poppet onto the valve seat and locks into position by a locking cam, creating a mechanical barrier to protect downstream equipment. Learn more about Fike’s Flow-Actuated Explosion Isolation Valve.

What is Explosion Venting?

A vent panel or group of panels provide a predetermined relief area installed in a specific location. Vent panels open at specified burst pressures (Pstat) to provide a quick release of the pressure generated from hot expanding gases, unburned material and flames to minimize damage to the enclosure, room or building. Fike offers a variety of composite, sanitary and grain elevator explosion vents.

  • Flameless Explosion Venting – Protective measure which will prevent the breakthrough of flames into the surrounding environment. Flameless venting is used to allow explosion venting in situations where the hazards of flames resulting from the venting action are not acceptable. Learn more about Fike’s flameless venting solutions.
  • Vent Discharge Duct – A duct that is added to explosion venting to direct the pressure generated from hot expanding gases, unburned material and flame resulting from a deflagration outside the building to a safe area.

Certifications/Organizations Questions

What is ATEX (Atmospheres Explosibles)?

A set of European Union regulations that are designed to ensure the safety of products being used in explosive environments. This approval agency has directives controlling explosive atmospheres.

What is CSB (Chemical Safety Board)?

Organization that investigates and reports on industrial incidents.

What is NFPA (National Fire Protection Agency)?

Create codes and standards for fire prevention, combustible dust and other hazards. Has no enforcement power or certifications of its codes and standards.

What is FM (Factory Mutual Global)?

Mutual insurance company that specializes in loss prevention services where risk and premiums are determined by engineering analysis. Provides FM approval on systems and hardware. Creates its own set of proprietary requirements and sizing methods for explosion protection.

Technical and Specs Questions

What is Burst Tolerance (Rupture Tolerance)?

The tolerance associated with the marked burst pressure within which the event is expected to burst. Usually expressed as a ± % of burst pressure or ± set pressure.

What is Combustion Area (Volume)?

The area (volume) where fuel and oxidant are present and ignition can occur.

What is Deflagration Index (KSt)?

KSt(measured in barg-m/s) is the deflagration index of a dust cloud (NFPA 68, 2018). Deflagration index is the rate of pressure rise in a standard, unvented spherical vessel and measures the relative explosion severity compared to other dusts.

What is Lower Flammable Limit (LFL)?

The lowest concentration of material that will propagate a flame from an ignition source through a mixture of flammable gas or combustible dust dispersion with a gaseous oxidizer (NFPA 654, 2017).

What is MAIT (Minimum Auto Ignition Temperature (dust cloud))?

Ignitibility value (measured in Celsius) which defines the minimum temperature at which a dust cloud will auto-ignite when exposed to heated air. Test procedure defined in ASTM E1491.

What is MEC (Minimum Explosive Concentration)?

Explosibility value (measured in g/m3) which defines the minimum concentration of a dust-air mixture that will propagate a deflagration. Also see Lower Flammable Limit (LFL). Test procedure defined in ASTM E1515.

What is MIE (Minimum Ignition Energy)?

Ignitibility value (measured in milliJoule) which defines the minimum ignition energy of a dust cloud in air by a high voltage spark. Test procedure defined in ASTM E2019.

What is MIT (Minimum Ignition Temperature)?

Ignitibility value (measured in Celsius) which defines the minimum temperature at which a dust layer will ignite. Test procedure defined in ASTM E2021.

What is Operating Ratio?

Ratio of the maximum system operating pressure to the minimum burst pressure associated with the explosion vent or rupture panel. Maximum Operating Pressure/Vacuum rating of a vent can be expressed as an operating ratio.

What is Particle Size (PSA)?

Procedure to determine the size range and average size of an operation’s dust particles.

What is Pmax?

The maximum pressure developed in a contained deflagration of an optimum mixture (NFPA 68, 2018).

What is Pred (Reduced Pressure)?

The maximum pressure developed in a vented enclosure during a vented deflagration (NFPA 68, 2018). FM 7-76 provides guidance when Pred is unknown. Pred can also be described as the maximum allowable pressure to prevent deformation of an enclosure or maximum allowable pressure that will result in an acceptable amount of deformation.

What is Process Temperature?

Maximum and minimum operating temperature within an enclosure or process.

What is TSP (Total Suppressed Pressure)?

Total Suppressed pressure (or reduced pressure) is a value calculated by using Fike proprietary software and the process data. It is the maximum momentary pressure that the vessel must withstand during a suppressed deflagration and must be compatible with the enclosure design strength. TSP may also be the pressure measured as a part of a test or in an actual suppressed industrial explosion. This value shall be provided to the customer per NFPA 69, 2014 Section 10.4.4

What is xMax/xMin (maximum/minimum isolation placement)?

The maximum/minimum safe installation distance from the process interconnection (or other specified place) which is calculated or determined for each specific application by Fike as required by NFPA 69, 2014.

Miscellaneous Questions

What is Airflow?

Unit of air flow through a process typically measured in cubic feet per minute (CFM).

What is Air Velocity?

Speed of which air moves through a duct, pipe or system. Can be calculated based on airflow and duct size.

What is Deflagration?

Propagation of a combustion zone at a velocity that is less than the speed of sound in the unreacted medium (NFPA 68, 2018).

What is Detonation?

Propagation of a combustion zone at a velocity that is greater than the speed of sound in the unreacted medium (NFPA 68, 2018).

What is a Duct?

Pipes, tubes or other enclosures used to convey materials pneumatically or by gravity (NFPA 652, 2016).

What is a Dust Hazard Analysis (DHA)?

A systematic review to identify and evaluate the potential fire, flash-fire and explosion hazards associated with the presence of one or more combustible particulate solids in a process or facility (NFPA 652, 2016).

What is a Dust Collector?

Generic identification of an air material separator using a media to separate particulate from an air stream (NFPA 652, 2016).

What is Isolation?

A method employing equipment (suppression and/or venting) and procedures that interrupts the propagation of a deflagration flame front past a predetermined point.

What is Metal Dust?

Any metal composed of distinct particles or pieces, regardless of size, shape or chemical composition, as a result from a solid state secondary processing operation that will burn (NFPA 484, 2015). Metal dust can have higher flame temperatures, requiring additional protection requirements.

What is an Oxidant?

Any gaseous material that can react with a fuel (gas, dust or mist) to produce combustion (NFPA 68, 2018).

What is Pressure (operating)?

Maximum operating pressure (positive and vacuum) within an enclosure or process.

What is a Primary Explosion?

The explosion in the process enclosure where the ignition occurs.

What is a Secondary Explosion?

The explosion in the process enclosure or surrounding area that is ignited by the explosion flame that enters through the connected pipeline and that was originally created by the primary explosion at the other end of the pipeline.

What is a Protected Area?

The area into which a deflagration will not be able to propagate on the upstream side of the isolation device.


In Fike’s continued effort to protect people and critical assets, we are excited to help you better understand explosion protection. Contact Fike’s explosion protection experts if you have questions about any of these terms or other terms important to your organization’s safety, or see more frequently asked questions about our solutions and operating procedures.