Watch videos with subtitles in your language, upload your videos, create your own subtitles! Click here to learn more on "how to Dotsub"

Inert Gas

0 (0 Likes / 0 Dislikes)
On February 28, 2004, the tanker Bow Mariner en route from New York to Texas exploded and sank in the Atlantic Ocean. Twenty-one crew members were killed. During the investigation, it was determined the cause of the accident was the ignition of a fuel and air mixture that was within its flammable limits. For a crew on any tanker, this serves as a sober reminder of the dangers they face. But with proper training in the handling of inert gases, these tragedies can be avoided. In this video, you will learn: what cause fire and explosions; how inert gas systems work; and the components that make up an inert gas system. There are three elements required to initiate and sustain combustion— fuel, oxygen, and an ignition source. All three combined can create a fire or explosion. Remove one of these elements and you can prevent an accident from occurring. The ratio of fuel and oxygen required varies with each combustible gas or vapor. The minimum concentration of a gas or vapor that will burn in air is known as the Lower Explosive Limit, or LEL. Below this level the mixture is too lean to burn. The maximum concentration of a gas or vapor that will burn in air is known as the Upper Explosive Limit, or UEL. Above this level the mixture is too rich to burn. The range between the LEL and the UEL is the flammable range for that gas or vapor. If the presence of an ignition source cannot be prevented within a cargo tank, the tank may be made inert by reducing the oxygen concentration to below that capable of combustion, reducing the fuel concentration to below the Lower Explosive Limit, or increasing the fuel concentration to above the Upper Explosive Limit. Inert gas is a gas or mixture of gases containing insufficient oxygen to support the combustion of hydrocarbons. Flammable vapors in cargo tanks are rendered inert by replacing the air with an inert gas. Depending upon the construction of the vessel, commonly used systems for producing inert gas include flue gas from the ship's boilers or a dedicated inert gas generator. The basic premise of an inert gas system is to reduce the level of oxygen in the cargo tank to a level that will not support combustion. Tanks should be made inert prior to loading cargo and monitored while at anchor and during sea passage. Inert gas is then continually generated during cargo discharge to ensure that the tank atmosphere remains within required oxygen and pressure limits. There are a few general requirements for inert gas systems. It must be capable of inerting, purging, and gas freeing empty tanks. It must also maintain the atmosphere in cargo tanks. Pressure is extremely important inside tanks. If you pull a vacuum into one of your tanks, you're basically drawing air which raises the O2 content of the atmosphere presenting a danger of creating an explosive environment. So maintaining pressure inside the tanks with your inert gas system is crucial to the safety of the vessel. Each individual cargo tank is fitted with its own pressure vacuum valve. These valves are designed to provide a layer of protection for tanks against rupturing or imploding due to the abnormal change in pressure caused by cargo operations, sea or atmospheric temperature changes, or malfunctioning pressure settings of the inert gas system. If the pressure in the cargo tanks increases or decreases past the set point, the PV valve will either release the pressure or allow for air to flow inward when the tank pulls a vacuum. As a backup safety device, a liquid pressure vacuum breaker is fitted to the piping on the deck and is designed to relieve pressure in the event that the tank's pressure vacuum valve exceeds its capacity during the operation of the inert gas system. Care must be taken not to allow a vacuum to develop which pulls oxygen-rich air into the tanks. For this reason, the inert gas supply must be maintained and oxygen content should be carefully monitored throughout cargo discharge operations. Tankers fitted with a fixed inert gas system must be provided with a closed ullage system. As a consequence of the Bow Mariner and other accidents, the inert gas requirements for oil and chemical tankers have been amended. The amendments have been included in the chapter 2, part 2 of the 1974 SOLAS Convention. It requires that an inert gas system shall be designed, constructed and tested to the satisfaction of the International Maritime Organization or IMO. All oil and chemical tankers of 8000 DWT and above must have a fixed inert gas system. The oxygen limit for inert gas supplied to cargo tanks has been reduced to 5%. To prevent tragedy such as the Bow Mariner, the crews should have a basic understanding of how an inert gas system works. Water pumps fill the deck seal and feed the different sections of the scrubber. The gases are passed through the pre-cooling section, then travel through the scrubber bottom tank. The water droplets carried by the gases are recirculated in the scrubber until the oxygen level falls below 5%. The main valve opens allowing the flow of gases to the cargo tanks at the same time the recirculation valve closes. The gases flow through the deck seal and past the vacuum breaker before being delivered to the tanks. The tank atmosphere is now inert and safe for cargo operations. Generally tanks are all tested prior to loading cargo. That is a very good practice to be getting into. That way you know exactly where you are before you load product. It's also a good idea throughout the load to also measure your tank atmospheres to see what's being produced as you're loading cargo. Tankers fitted with an inert gas system should have their cargo tanks kept in a nonflammable condition at all times. In this video we learned: what causes fire and explosions: how an inert gas system works; and what are the components in an inert gas system. The inert gas system ensures that you and the rest of your crew will have a safe and successful voyage.

Video Details

Duration: 8 minutes and 45 seconds
Country: Andorra
Language: English
License: Dotsub - Standard License
Genre: None
Views: 7
Posted by: maritimetraining on Feb 13, 2017

Inert Gas

Caption and Translate

    Sign In/Register for Dotsub to translate this video.