When measuring the oxygen content of cargo tanks, where should you take the readings?

Taking oxygen readings in cargo tanks is critical for assessing the safety and stability of the stored materials, as well as for preventing explosive conditions. The correct practice involves measuring the oxygen levels at positions that provide a good representation of the atmosphere within the tank.

Measuring at one half the ullage of the tank provides an understanding of the conditions in the space that could be most hazardous. The ullage is the space above the liquid where vapors accumulate, and it is important to monitor the oxygen content in that area, as it is directly affected by vapor generation and can indicate the risk of combustion in the event of a hazardous material.

Additionally, measuring one meter below the tank top captures the potential for stratification or layering effects in the vapor space, where different concentrations of gases can exist at various heights. This interval is crucial because gases can be denser or lighter depending on their composition, affecting the oxygen levels.

Therefore, by taking readings at both one half the ullage and one meter below the top of the tank, you are effectively covering key areas where oxygen levels can present a risk, ensuring a comprehensive understanding of the tank's atmosphere. This practice supports maintaining safety standards and managing the risk of fire or explosion during operations involving the cargo.