The exhausters. The coal gas is a lazy gas that needed some pressure in order to complete its journey through the facilities. That pressure was provided by two exhausters that pulled the coal gas from the retort tanks and forwarded it to the production line’s next step, the purification. The exhausters had another very important role, besides that. They prevented the coal gas from leaking back into the retorts where the workers opened the lids of the retorts in order to refill them with coal.