The practice of loading one type of petroleum product into a tank truck compartment that has previously carried a different type of product.
The practice is generally discouraged and is, in fact, banned by fire regulations in many jurisdictions. The problem created by switch loading is that a relatively safe fuel like home heating oil, with a high flash point, can become contaminated with an easily ignited fuel like gasoline. The accumulation of static electricity is also accelerated in a switch-loading operation. This, in turn, can increase the likelihood of a static electricity discharge, capable of igniting vapors in the tank compartment.
If switch loading is unavoidable, there are techniques that can be used to reduce generation of static electricity. These techniques include use of reduced fill rates.