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Procedures Associated with Cargo Tank Entry in Ships – The Inert Gas (IG) Perspective

written by: Ricky • edited by: Lamar Stonecypher • updated: 3/13/2009

We normally do not think twice before entering any enclosed space in our routine every day life but not so on ships. Just read this article to find out what precautions are necessary if one has to enter cargo tanks for inspection or repairs.

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    Introduction

    We studied about the crude oil washing operation on tanker ships in our previous article. In this article we will learn about the precautions associated with entering empty cargo tanks on board a ship.

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    Tank Entry - Procedures & Precautions

    Have you ever thought that there could be procedures associated with a simple thing as entering a tank? If not then you better know that on ships (this applies to situations on land as well) whenever you enter any empty tank or enclosed space for that matter, you need to follow certain precautions so that your entry and exit from the tank are safe for you and other personnel.

    What possible dangers do you foresee in an empty cargo tank of the ship? If you are thinking in terms of sharks or whales then you can rest assured about it. But you have forgotten about the deadly invisible enemy, namely the atmosphere inside the tank which could either contain flammable hydrocarbons or less quantities of oxygen due to their inert or nearly inert conditions. This certainly means deadly results for those who dare to venture carelessly into such spaces.

    So whenever a cargo tank needs to be entered all the inert gas is blown out by the procedure of gas freeing the tank using powerful but portable blowers at suitable place depending on tank structure and location of inlet and outlet points. All the pipelines leading in or leading out of the tank should be closed tightly and wherever possible blanks should be inserted to prevent accidental leakage of any inert gas or other fluids into the tank which could contaminate the atmosphere and put the lives of people inside in danger.

    After gas freeing the tank it is necessary to take samples at the points which are farthest away from entry/exit points in order to ensure that the worst points are safe and the values of these samples should be analyzed to find out the oxygen and combustible gas levels which should be 21% and <1% respectively. Breathing apparatus should also be used in doubtful conditions and even if it is not donned, it should be kept as a standby.

    Other procedures include fulfilling checklists for tank entry which lists various important tasks such as proper communication, standby people at outlets and so forth. The details of the procedures have been laid down and published by the International Chamber of Shipping and the Oil Companies International Marine Forum in the form of a manual which goes by the name of ISGOTT or International Safety Guide for Oil Tankers & Terminals. Some of these procedures and precautions can be found in sections of chapter 9 while the remaining ones are dealt with in chapter 10 of this guide.

    In the next article, we will see what all dangers could result from the presence or absence of different gases inside the tank

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