Looking for a new Dust Collector?

If you’re investigating the use of a dust collection system, one of the first things you’re going to want to do is determine the explosive characteristics of the dust you’re dealing with, as well as how severe such an unmitigated explosion may be. With this information in hand, you’ll be able to properly spec in the associated equipment, and make certain that you and your coworkers are properly protected.

With that in mind we’ve highlighted a few key terms and phrases that will aid you in your discussions with your team members, and prospective vendors. Naturally, we’d like to be the vendor of choice for such projects, but we understand the need to do a little due diligence.

So, in a nutshell, here are a few things to consider:

Kst Values, Pmax, and ST Class

You’re bound to hear these terms more than once during your consultations. In short, these are explosive properties as measured in a laboratory environment to quantify the severity of a potential dust explosion.

The explosion indices test follows BS EN 14034-1:2004 - to determine the maximum explosion pressure (Pmax) of a dust cloud; and BS EN 14034-2:2006 – to determine the maximum rate of explosion pressure rise of a dust cloud (Kst).
The tests are caried out in a 20-litre sphere, which reproduces a high state of turbulence with a mind to simulate a worse-case scenario.

Here is how it works. A weighted quantity of combustible dust is placed into the dust container. The main explosion chamber is then evacuated to 0.4 bar absolute, followed by an automatic test sequence to pressurize the dust container to 20 bar gauge. At this point a fast-acting valve on the dust container outlet is opened to allow material to enter the explosion chamber. A rebound nozzle ensures an even distribution of the dust within this chamber, while the control system activates two 5 KJ chemical igniters at the centre of the sphere 60 ms after the dust has been properly dispersed.

Explosion pressures are measured for a range of dust concentrations using piezo-electric pressure transducers. The tests are carried out over three series to ensure a firm understanding of the explosive properties of the dust being tested. From here the arithmetic mean of the maximum values (both maximum pressure & the maximum rate of pressure rise) is determined.
The Kst value is calculated as the equivalent pressure in a 1 m³ sphere from the cube law (Kst value = cube root of volume x explosion pressure rise).

The ST Class is based on the Kst values as follows:
ST Class 0 – Kst value = 0
ST Class 1 – Kst value less than 200 bar m/sec
ST Class 2 – Kst value between 200 and 300 bar m/sec
ST Class 3 – Kst value greater than 300 bar m/sec

These results are essential for validating the protection design of the equipment you’re looking to install. This may include such things as explosion venting, explosion suppression, as well as explosion containment.

Say, for example, you’re dealing with aluminum dust. Just how explosive is it? Aluminum dust often comes with an ST3 designation, which make it very explosive. For those applications you’re going to want to follow strict safety guidelines, as well as employ proper explosion mitigation and containment as it pertains to dust collection for your facility.

There is a lot more that can be said about Pmax, Kst, and ST Ratings, but this will give you a pretty good framework to get started. Should you have any questions please feel free to reach out. We’re here to help.