Toxic and inflammable gases must be diluted to a safe level; dust and smoke dispersed; excessive heat should be relieved; and escape routes must be kept clear from smoke. Pollution emitted by trains and road vehicles must be removed to provide an acceptable and safe environment. The heat from a train may need to be removed by forced ventilation to ensure that the temperature is acceptable to both people and equipment.

Length of exposure and concentration of carbon monoxide are the important factors in the progressive effects of loss of alertness, headache and unconsciousness. Other products of car exhausts such as nitrogen and sulphur oxides can also have negative health effects of drivers.

As vehicles become cleaner and more efficient and alternative fuel sources become more common, the day to day ventilation requirement for tunnels will change meaning far more focus is required on the fire safety element of tunnel ventilation for the long term safety of users.