To limit the probability of the transmission of excessive noise or vibration, which could lead to occupants disabling the supply fans, which could lead to excessive negative pressure (where supply fans alone are disabled), which could lead to the spillage of carbon monoxide gas from fuel-burning appliances that are susceptible to spillage, which could lead to the acute poisoning or asphyxiation of persons.
To exempt fans and heat recovery ventilators fixed only to a concrete base from the requirement to install resilient mountings, on the basis that concrete is unlikely to transmit vibration generated by the equipment to occupied space.