If the available natural ventilation in shafts and canal systems is not sufficient due to local conditions, such as position of the shafts or their cover conditions, additional technical ventilation measures are required. Especially in warm temperatures, when the air in the shaft is cooler than in the environment, no sufficient ventilation is ensured any more. Temporary opening of the shaft cover will not always ensure ideal ventilation. In sewer shafts, for example sewer gases may lead to a displacement of oxygen in the air and thus can lead to unconsciousness in canal work.
Remedy may be provided here by targeted technical ventilation and powerful ventilators. Fresh air gets directly to the work place and prevents health affects caused by bad air.
Sufficient technical ventilation is achieved when an air flow of at least 600 cum/h per square metre of sewer cross-section is ensured.