Another cause of oxidation is the practice of sweeping the tank floors (especially in ship tanks). This may have to be carried out for palm oil during discharge for complete emptying of the tank. Sweeping is normally done by 5–7 people who will have to go down into the tank to physically push the oil towards the sump or discharge vent. The act of scraping the tank wall and floor will cause loose rust and tank coating to peel off, thereby increasing the iron contamination of the oil. Very often the sweeping is also carried out in conjunction with jet spraying or re-circulate hot oil. This will further cause aeration of the oil.
Aeration of the oil could also occur as a result of faulty or poorly maintained pumps with faulty glen seals or as a result of other leakages.