Explain the use and limitations of Explosimeter on oil tankers ?

• As the explosimeter only indicates the presence of flammable gases and vapours it may be dangerous to enter the compartment as no indication of toxicity is given or sufficiency of oxygen.
• A compartment which is initially safe may be rendered unsafe by future operations e.g. stirring or handling bottom sludge in a crude oil tank. Hence, frequent tests are required while the work in progress.
• If a compartment having a high boiling point liquid is heated by welding or other processes the vapour concentration will increase and such an atmosphere which originally showed a low concentration vapour may now be rendered explosive.
• When testing at a high temperature some of the vapour may condense in the sampling tube of the instrument, so only a small concentrate of vapour will be indicated by the instrument.
• As the instrument depends on combustion of the flammable portion of the sample it cannot detect in a steam or inert atmosphere due to the absence of O2.

In the case of inerted tanks of vessels carrying crude or refined petroleum products an instrument called a tankscope has been specially designed to detect and measure the concentration of hydro carbon vapour in the absence of oxygen.