Partial Inerting - A Cost Efficient weapon against Dust Explosion

Hey everybody, hope you are enjoying my blog and finding the information useful in your field of work. Today we are talking about a topic which is rather less explored and understood in many industries as of now i.e. "Partial Inerting".

Let's start first with understanding Inerting. Inerting is defined as the replacement of "oxidant" in a system by a non-reactive, non-flammable gas, to make the atmosphere within the system unable to propagate flame. Inerting may be achieved by using a non-flammable gas, which will neither react with the fuel nor with the oxidant. There are many gases used for inerting such as Nitrogen, Carbon Dioxide, Flue Gases, Noble Gases (Argon, Helium), etc.

P.S: Some material may react with these inert gases under some conditions. Hence, correct selection of gases is critical.

Now let's discuss the concept of PARTIAL INERTING to prevent dust fire and explosion. Partial Inerting means dilution of oxidising atmosphere with an inert gas but not up to the extent of LOC i.e. oxidant concentration lies between LOC and atmospheric concentrations. In other words, for partial inerting, the oxidising atmosphere (most often air) in which the explosible dust is dispersed is mixed with a fraction of inert gas (e.g. nitrogen) considerably smaller than that required for complete inerting (i.e. below LOC). 

Can Electrostatic Discharge (ESD) from Non-Conductive Bags act as an Ignition Source?

Hope you are enjoying the posts and able to gain some insights from the blog.

Now for this week blog, I am touching on a more sensitive question, which people have asked me in almost all Electrostatic Hazard Seminars. "Can Non-Conductive Bag act as an ignition source?"

A non-conductive bag, being an insulator can act as a source of Brush Discharge which has approximate energy of up to 3-4 mJ associated with it. Depending on the type of flammable atmosphere, brush discharge from the non-conductive bag may/ may not act as an ignition source.

Based on the equivalent energy of brush discharges, it must be assumed that most potentially explosive gas/air mixtures, solvent vapor/air mixtures and hybrid mixtures (vapor/gas and dust with air) can be ignited by brush discharges.

Are there two types of Minimum Ignition Energy (MIE) for powders?

Here we go. The first blog; let’s begin the blogging and sharing together.

Yes, there are two types of MIE, where one type is carried out without inductance and the other is carried out with inductance.

Minimum Ignition Energy is the minimum energy that is required for ignition of fuel. In other words, the minimum energy an ignition source must provide to the fire triangle for the fuel to burn in presence of an oxidant.
The test to establish MIE is carried out in an apparatus called MIKE3 (refer image below). It is performed using ASTM E2019, “Standard Test Method for Minimum Ignition Energy of a Dust Cloud in Air” or EN13821 “Potentially explosive atmospheres — Explosion prevention and protection — Determination of minimum ignition energy of dust/air mixtures”

MIE (Without inductance) corresponds to the energy required by electrostatic discharge to ignite a dispersed cloud. The circuit of MIKE3 for this test is purely capacitative and the spark energy can be related straight to 1/2*C*V^2 based on the capacitance selected.

MIE (With inductance) simulates the longer duration discharges from electronic circuitry that can occur from machines or control equipment (essentially a spark from short in a wire or electronic equipment) or mechanical sparks, by adding an inductance in the existing circuit.

Now one thing to remember is that MIE (With Inductance) is more conservative as compared to MIE (Without inductance). 

Next question that comes is which one to choose?