Britannia Airways, based at Luton Airport, has to maintain a permanent constant humidity level in its computer rooms and hangars in order to eliminate the build up of static electricity. The effi ciency of the humidifi ers supplied by Vapac and J.S. Humidifi ers Ltd was being severely compromised by the continual formation of heavy scale. The humidifiers required descaling within one month of installation and the deposit was so hard that only acid cleansing was effective. This involved a twenty four hour operation and the careful disposal of acid waste. The progressive damage to the metal heating elements reduced their effective life to only 3 months.