Question

Disadvantages of cleveland open cup apparatus

Answer 1

The Cleveland open-cup method is used to determine the flash point of a petroleum product with the help of a Cleveland open-cup tester.

Disadvantages

1. It lacks precision. 

2. It gives a higher flash point than a closed cup as it allows free loss of vapours to the atmosphere.

Answer 2

Cleveland open cup apparatus actually gives the less accurate value for determination of flash point of different petroleum product.
As the name indicate such test cup are open mostly, So the chances are there that the surrounding environment can effect the result if it is not controlled.
Due to being open the cleveland open cup can affect the result as the loss of vapours to the atmosphere could happens ( vapours causes the flashing or ignition).