CO2 is an inert gas, which means it does not explode. The CO2 used by the SoluCalc is food-grade CO2. It is the same CO2 that is used to make sparkling water (Sodastream, etc.) and in cafes and restaurants for beer taps.
You just have to know that CO2 is a gas heavier than air, so it tends to fill rooms from below.
Assuming a 10 kg bottle of CO2 suddenly emptied into a sealed room at the very bottom of the building, the volume of CO2 would reach 4.5 m³ of CO2 in the air.
It would fill about 30 cm from the floor in a 15 m³ room, and those 30 cm would contain no oxygen.
You might want to avoid crawling next to the cylinder if such a situation was to arise.