The following ambient conditions shall be observed during measurements and shall determine whether testing is to occur or not:

(1) Wind. Sound level measurements shall not be made when the wind speed is in excess of:

(a) 20 mph (32 km/hr) for the close proximity test, WAC 173-58-080;

(b) 12 mph (19 km/hr) for all other tests.

(2) Precipitation. Sound level measurements shall not be made when precipitation is falling in such a way as to affect the equipment or the measurement readings.

(3) Background sound level. Sound level measurements shall not be made when the difference between the background sound level and the level of the measured sound source is less than 10 dBA, unless, the measurement personnel are technically qualified to logarithmically subtract the background level from the measured source's sound level.