# Influence of the Pyrotechnic Igniter Composition Aging on Explosion Parameters of Dispersed Dusts
## 3 Results  
The experiment described in the article studied the possible influence of storage period under common conditions (15-30 \({}^{\circ}\)C, humidity 40-60% RH) on degradation of the pyrotechnic charge of the Sobbe igniter. Igniters manufactured in 2021 and in 2018 were used for the measurement. The storage period of the igniter manufactured in 2021 was less than 1 year. The storage period of the igniter manufactured in 2018 was more than 2 years (up to 3 years). Igniter 1 and Igniter 2 were selected based on the data provided by the manufacturer, who recommends using the igniter within two years from the date of manufacture, see Figure 5. The current paper does not study the aging process of the pyrotechnic composition in the SOBBE igniter. The aging process of a pyrotechnic composition can be determined, e.g., according to the Pyrotechnic materials--Directive 2013/29/EU-EC Other pyrotechnic articles (category P1 and P2)--EN 16263. However, the pyrotechnic composition used in the igniter is extremely dangerous (handling, friction, sparks, fire, etc.), and its properties and parameters can be determined only in a workplace equipped with specific technology for the given purpose, material support and authorised staff.  
The measurement was performed with three dust samples at the concentrations of 250 and 500 g\(\cdot\)m\({}^{-3}\) in the KV 150M2 explosion chamber and in the 20 L sphere explosion chamber.  
Pressure records to compare the course of the explosion of overpressure P and rate of pressure rise dP/dt of the _Lycopodium clavatum_ sample in the KV 150M2 chamber are shown in Figures 6 and 7 (for the concentration of 250 g\(\cdot\)m\({}^{-3}\)), and in Figures 8 and 9 (for the concentration of 500 g\(\cdot\)m\({}^{-3}\)).  
Figure 4: Cross section of commercially available igniter (redrawn according to patent application Chemical detonator with electric trigger—US 2016/0102957 A1 [27]) 1—pyrotechnic composition filling, 2—plastic case, 3—metal case, 4—stopper, 5—fuse head, 6—fuse head sealing, 7—priming wires.  
Figure 5: Sobbe igniter label.  
Figure 6: Overpressure P and rate of pressure rise dP/dt of 250 g\(\cdot\)m\({}^{-3}\)_Lycopodium clavatum_ powder, ignited by Igniter 1 (shelf life less than 1 year).  
Figure 7: Overpressure P and rate of pressure rise dP/dt of 250 g\(\cdot\)m\({}^{-3}\)_Lycopodium clavatum_ powder, ignited by Igniter 2 (shelf life more than 2 years).  
A sample of benzoic acid and magnesium powder was measured in a 20 L sphere blast chamber. The comparison of the measured explosion parameters with the deviation is shown in Table 1.  
The value of the explosion constant \(\mathrm{K_{st}}\) is calculated by the formula  
\[\mathrm{K_{st}}=\sqrt[3]{\mathrm{V}}\times\left(\frac{\mathrm{dP}}{\mathrm{dT} }\right)_{max} \tag{2}\]  
The explosion constant for a standard sample of _Lycopodium clavatum_ (Igniter 1) at a concentration of 250 and 500 g\(\cdot\)m\({}^{-3}\) is calculated as  
\[\mathrm{K_{st,250,\,igniter 1}}=\sqrt[3]{\mathrm{V}}\times\left(\frac{\mathrm{dP}}{ \mathrm{dt}}\right)_{\mathrm{max}}=\sqrt[3]{0.365\mathrm{\ m^{3}}}\times 182.7 \mathrm{\ bar\cdot s^{-1}}=130.6\ \mathrm{\ bar\cdot m\cdot s^{-1}} \tag{3}\]  
\[\mathrm{K_{st,500,\,igniter 1}}=\sqrt[3]{\mathrm{V}}\times\left(\frac{\mathrm{dP}}{ \mathrm{dt}}\right)_{\mathrm{max}}=\sqrt[3]{0.365\mathrm{\ m^{3}}}\times 208.5 \mathrm{\ bar\cdot s^{-1}}=149.0\ \mathrm{\ bar\cdot m\cdot s^{-1}} \tag{4}\]  
Figure 8: Overpressure P and rate of pressure rise \(\mathrm{dP/dt}\) of 500 g\(\cdot\)m\({}^{-3}\)_Lycopodium clavatum_ powder, ignited by Igniter 1 (shelf life less than 1 year).  
Figure 9: Overpressure P and rate of pressure rise \(\mathrm{dP/dt}\) of 500 g\(\cdot\)m\({}^{-3}\)_Lycopodium clavatum_ powder, ignited by Igniter 2 (shelf life 2 years).  
The value of deviation is calculated by the formula  
\[\delta=\frac{\text{value}_{\text{igniter2}}-\text{value}_{\text{igniter1}}}{ \text{value}_{\text{igniter1}}}\times 100 \tag{5}\]