What class of permissible explosives releases the smallest volume of poisonous gases?

Class A explosives are characterized by their low hazard level and are known for producing the least volume of toxic gases compared to other classes. This is crucial in mining environments, where minimizing the release of poisonous gases is vital for the safety of workers and the surrounding environment.

Class A explosives typically include materials that are less sensitive and have a lower energy output, which translates to a reduced risk of harmful emissions during detonation. This is particularly important in confined spaces, such as mines, where the accumulation of hazardous gases could pose serious health risks to miners.

In contrast, Classes B, C, and D explosives vary in their compositions and intended uses, leading to higher emissions of poisonous gases during detonation. Therefore, Class A is favored in situations where safety from toxic exposure is a priority, making it the correct answer in this context.