Pmax AND (dP/dt)max

 

[EN 14034-1 and 14034-2; ASTM E 1226]

 

The powder to be tested is blown into a 20-ℓ-Apparatus and the resulting dust cloud is ignited with two chemical igniters, having a total ignition energy of IE = 10.000 J.

 

The ignition delay time (turbulence level) in the 20-l-Apparatus is tv = 0,06 s.

 

The pressure inside the sphere is recorded.

 

By variation of the dust concentration, the most critical conditions are determined (three test series).

 

To characterize the explosion of the powder Pmax and Kmax are determined.

 

Kmax is the maximum rate of pressure rise normalized for a container size of 1 m.

 

Kmax = (dP/dt)max x V1/3 [barm/s]

 

Pmax is the maximum explosion overpressure starting from an initial pressure of 1 bar.

 

Based on the Kmax values the dust is classified into several dust explosion classes St:

 

Dust explosion constant

Kmax [barm/s]

Dust explosion class

St

Maximum explosion overpressure

Pmax [bar]

0 < Kmax 200

St 1

10

200 < Kmax 300

St 2

10

Kmax > 300 St 3 12

 

Pmax and Kmax or the dust explosion class St are the basis for the design of constructive explosion protection measures.