Wilhelm  Jost  Institut Förderverein e.V.

Maximum explosion pressure and maximum rate of pressure rise



The explosion overpressure pm and the rate of pressure rise dp/dt describe the violence of reaction of dust/air mixtures of random concentration after ignition in a closed vessel. The maximum explosion pressure pmax and the maximum rate of pressure rise (dp/dt)max of combustible dusts are determined in closed standard equipment by means of tests over a wide range of concentration.


A dust is not combustible in the form examined in each case (e.g. refinement, dampness), if no inflammation arises over a far concentration range (at least of 30 - 2000 g/m³).  A material only can be classified as "not dust explosionable" if exotherms oxidation reactions are excluded from its chemical condition or if the investigations concerning the explosibility of fine dust (< 63 µm) also led to no explosion.


The maximum rate of pressure rise depends on the volumen. The product of the maximum rate of pressure rise and the third root of the special volume is constant (Cubic Law) and is called KSt-value.


In accordance to the K-values different dust explosion classes can be defined:



Dust explosion class

KSt-value < 200 bar m s-1

St 1

200 bar m s-1 < KSt-value < 300 bar m s-1

St 2

KSt-value > 300 bar m s-1

St 3


The dust explosion classes give only a hint concerning the dimensioning of preventive concepts/ design measures of explosion protection.


Testing Method:


according to BG Chemie R 003 6/2000 in a 20-L-apparatus or in an 1 m³-vessel

(Further information see also Fire and Explosion Protection)



Safety-relevant meaning:


These datas are needed for the machine interpretation and for constructional explosion prevention.


Preventive measure

considered safety technial index

Explosion Pressure Resistant Design

maximum explosion overpressure

Explosion Pressure Relief

maximum explosion overpressure, KSt-value

Explosion Suppression