C.2 Dynamic Characterization Properties
273
numbers, with values of 1–3 representing that it is not fire spreading and values
of 4–6 representing that it is.
6. Dynamic Explosion Parameters: include the maximum explosion pressure
(P max ) and the cubic law constant (K max ). These are determined through
centrally igniting the substance in a closed spherical testing apparatus. The
maximum explosion pressure (P max ) is the pressure measured for a dust or
vapor cloud at its most optimal concentration. According to the ideal gas law,
at constant volume Eq. C.1 shows how P max is based on the initial conditions
of the pressure (P 0 ), the amount of combustible material (n 0 ) in mols, and the
temperature of the reaction (T 0 ). After the explosion, the temperature T max is
reached through an adiabatic rise in temperature (T max = T 0 + T ad ). n max
represents the amount of material after the reaction in mols:
P max =
P 0 × n max × T max
n 0 × T 0
(C.1)
The cubic law constant (K max ) characterizes how fast the pressure from
a deflagration or explosion rises in an enclosed vessel. This index is used
to properly size explosion vents and design explosion suppression systems.
Equation C.2 shows the cubic law for determining the value of K max , where
the maximum change in pressure (P ) per time is multiplied by the cubic root of
the volume (V ) of the testing apparatus. Linearly with the scale-up factor (V
1
3 )
of the critical equipment, the maximum increase of the explosion pressure is
reduced since K max is constant and unique to the mixture of the materials:
K max =
dP
dt
max
× V
1
3
(C.2)
A smaller K max value results in more time until the maximum pressure is
reached, and it is important for safety devices to have enough time to properly
react before an explosion occurs. As P max is proportional to the normal pressure
of the system, critical reactions such as the oxidation of hydrocarbons should
ideally take place at the lowest pressure possible. Table C.1 shows an example
set of P max and K max for some common substances. The values in this table are
based on a P 0 at 1 atm (101,325 Pa). It can be seen that for combustible mixtures
at atmospheric pressure, the P max is not extremely high and an appropriately
appropriately pressure-resistant device would therefore be feasible to construct
(but not for dusts).
The following specific dust hazard classes have also been set to categorize
the hazard on the basis of K max :
• ST 0: K max = 0 bar m s −1
• ST 1: 1 ≤ K max ≤ 200 bar m s −1
• ST 2: 201 ≤ K max ≤ 300 bar m s −1
• ST 3: K max > 300 bar m s −1
273
numbers, with values of 1–3 representing that it is not fire spreading and values
of 4–6 representing that it is.
6. Dynamic Explosion Parameters: include the maximum explosion pressure
(P max ) and the cubic law constant (K max ). These are determined through
centrally igniting the substance in a closed spherical testing apparatus. The
maximum explosion pressure (P max ) is the pressure measured for a dust or
vapor cloud at its most optimal concentration. According to the ideal gas law,
at constant volume Eq. C.1 shows how P max is based on the initial conditions
of the pressure (P 0 ), the amount of combustible material (n 0 ) in mols, and the
temperature of the reaction (T 0 ). After the explosion, the temperature T max is
reached through an adiabatic rise in temperature (T max = T 0 + T ad ). n max
represents the amount of material after the reaction in mols:
P max =
P 0 × n max × T max
n 0 × T 0
(C.1)
The cubic law constant (K max ) characterizes how fast the pressure from
a deflagration or explosion rises in an enclosed vessel. This index is used
to properly size explosion vents and design explosion suppression systems.
Equation C.2 shows the cubic law for determining the value of K max , where
the maximum change in pressure (P ) per time is multiplied by the cubic root of
the volume (V ) of the testing apparatus. Linearly with the scale-up factor (V
1
3 )
of the critical equipment, the maximum increase of the explosion pressure is
reduced since K max is constant and unique to the mixture of the materials:
K max =
dP
dt
max
× V
1
3
(C.2)
A smaller K max value results in more time until the maximum pressure is
reached, and it is important for safety devices to have enough time to properly
react before an explosion occurs. As P max is proportional to the normal pressure
of the system, critical reactions such as the oxidation of hydrocarbons should
ideally take place at the lowest pressure possible. Table C.1 shows an example
set of P max and K max for some common substances. The values in this table are
based on a P 0 at 1 atm (101,325 Pa). It can be seen that for combustible mixtures
at atmospheric pressure, the P max is not extremely high and an appropriately
appropriately pressure-resistant device would therefore be feasible to construct
(but not for dusts).
The following specific dust hazard classes have also been set to categorize
the hazard on the basis of K max :
• ST 0: K max = 0 bar m s −1
• ST 1: 1 ≤ K max ≤ 200 bar m s −1
• ST 2: 201 ≤ K max ≤ 300 bar m s −1
• ST 3: K max > 300 bar m s −1