 A single-blade shutter designed to rotate at very high speed (up to 3,600 RPM) doubles as a cooling fan.Unlike other projectors of its hi-power kind, the DP70 did not offer forced-air cooling of the film itself, which is known to be a key feature to prevent overheating of the film and the major nitrate-fire prevention measure.A water cooled pre-shield just assists in keeping the gate and metal parts cold, not the film.