In 1984 the track was wet before the race. Niki Lauda was concerned with the transition from wet to a dry and oily track on wet, wet weather tires. (When the rain starts it will release oils in the bitumen from the dry track. The oils are usually washed off rather quickly by more rain, but not on covered track.)
Niki spoke to Bernie Ecclestone and asked for the tunnel to be sprayed with water. Bernie agreed and asked the local fire truck to spray down the tunnel.
Needless to say, the water didn’t last long and a dry line appeared shortly into the race.
Note: I was unable to find a photo or video of the actual water being sprayed if you can find it please share with me!