Before crude oil washing a tank, the oxygen content must be measured at what distance from the deck?

Before proceeding with crude oil washing a tank, it is essential to ensure that the oxygen content is safe and at appropriate levels to prevent any fire or explosion risk. The measurement of oxygen content is typically conducted at a distance of one meter from the deck. This distance is chosen to provide a reliable indication of the air quality in the tank's upper atmosphere where vapors can accumulate and where workers might be present during the washing process. Measuring at this distance helps ensure that the readings accurately reflect the conditions that personnel may be exposed to, allowing for the implementation of appropriate safety measures before the washing operation begins.