“It’s been a long time since we’ve seen such an explosive dust,” this is how a WOLFF GROUP expert commented on the test dust explosion based on paracetamol. “The pretext for the experiment is our work preparing a risk assessment document and an explosion hazard assessment for one of manufacturers from the pharmaceutical industry,” – he continued.
The secondary explosion is even more dangerous than the primary one
In the video, we see two tanks with a volume of 0.05 cubic meters each. The tanks are connected by a channel and contain about 200 grams of paracetamol-based dust used in the manufacture of popular painkiller pills.
Each of the tanks has a safety feature in the form of a bursting element, which is intended to vent excessive pressure and flame to the surroundings at the time of explosion. In this case, they have been significantly oversized for safety.
Consequences of secondary explosion
What you should pay special attention to is the channel that connects the two tanks. It does not have the so-called explosion cut-off, and thus the flame and explosion pressure propagate from the right to the left tank, where the so-called secondary explosion occurs. This is very dangerous. Our expert explains in detail why this is happens (see yellow box below).
There are several reasons why a secondary explosion can have much more serious consequences than a primary one. This is because its maximum pressure and dynamics is higher – says an expert from WOLFF GROUP, a company specializing in the field of explosion safety. This can lead to serious consequences, including bursting of the apparatus in which the secondary explosion occurred even if it had explosion protection such as an explosion relief or suppression system. These systems are initially chosen for specific parameters, which are increased in the case of a secondary explosion.
There are four phenomena to consider in a secondary explosion:
- The secondary explosion starts at a higher pressure, which eventually increases the maximum explosion pressure
- The pressure wave of the first explosion causes turbulent movement of the dust-air mixture, which improves combustion conditions
- The ignition source in a secondary explosion has a much larger volume and energy and therefore contacts more flammable particles at any one time and can ignite a mixture with a higher concentration
- This phenomenon can both improve and worsen combustion conditions. As the concentration of dust in the air increases, its particles come closer together, making it easier for one particle to ignite another. However, once the optimum concentration is exceeded, due to insufficient amount of oxidant between the molecules, combustion conditions deteriorate.