The prima facie speed limitations set forth in R.C. § 4511.21 or a substantially similar municipal ordinance do not apply to emergency vehicles or public safety vehicles when they are responding to emergency calls and are equipped with and displaying at least one flashing, rotating, or oscillating light visible under normal atmospheric conditions from a distance of 500 feet to the front of the vehicle, and when the drivers thereof sound audible signals by bell, siren, or exhaust whistle. This section does not relieve the driver of an emergency vehicle or public safety vehicle from the duty to drive with due regard for the safety of all persons using the street or highway.
(R.C. § 4511.24) (`80 Code, § 434.06)