Why We Need To Purge The Cargo Tanks Before Making Them Gas Free

Summary

This educational video from 'My Time Genie' delves into the critical process of purging hydrocarbons from oil tanker cargo tanks to ensure safety. It explains the dangers of hydrogen sulfide and hydrocarbons, and the importance of using inert gas to purge these gases before introducing fresh air. The video outlines three purging methods: displacement, dilution, and positive displacement, aiming to reduce hydrocarbon levels below 2% to avoid flammability. It emphasizes the use of HC detectors to measure the safety of the tank's atmosphere and inert gas, ensuring a safe environment for gas freeing operations.

Takeaways

• 🚢 The atmosphere inside a cargo tank on an oil tanker can be lethal due to gases like hydrogen sulfide and hydrocarbons.
• 🌬️ 'Perching purging' is a procedure used to expel dangerous gases from cargo tanks by introducing inert gas.
• ⛔ Hydrogen sulfide is purged to reduce its level to a point that is safe for human life.
• 🔥 Hydrocarbons are purged to prevent the risk of explosion when mixed with oxygen.
• 🔍 Punching a cargo tank is necessary before purging to avoid creating a flammable mixture with the introduction of fresh air.
• 🔄 The three stages of purging a cargo tank are: too rich (can't catch fire), flammable range (risk of fire or explosion), and too lean (safe from fire or explosion).
• 🛠️ There are three methods for purging hydrocarbons: displacement, dilution, and positive displacement.
• 💡 Inert gas is used because it lacks both hydrocarbons and oxygen, preventing the atmosphere from becoming flammable.
• 🔍 A hydrocarbon (HC) detector is crucial to ensure the atmosphere in a cargo tank is below 2% HC before introducing fresh air.
• 🌟 Once the HC level is confirmed to be below 2%, it's safe to introduce fresh air and proceed with gas freeing the cargo tank.

Q & A

What is the primary danger of the atmosphere inside a cargo tank on an oil tanker?

The atmosphere inside a cargo tank can contain hydrogen sulfide, which is dangerous for human life, and hydrocarbons, which are not only harmful if inhaled but can also lead to an explosion.

What is the purpose of purging in the context of oil tankers?

Purging is done to expel dangerous gases like hydrogen sulfide and hydrocarbons from a cargo tank, making it safe for human entry and preventing potential explosions.

Why is it crucial to reduce the hydrogen sulfide level in a cargo tank?

Reducing the hydrogen sulfide level ensures that it is no longer dangerous to human life in case it escapes onto the main deck of the tanker.

What is the significance of reducing the hydrocarbon percentage in a cargo tank before making it gas-free?

Reducing the hydrocarbon percentage prevents the atmosphere inside the tank from becoming flammable when mixed with oxygen, thus avoiding the risk of fire or explosion.

Why is it incorrect to assume that introducing fresh air into a cargo tank will automatically expel all dangerous atmospheres?

While fresh air will expel the atmosphere, it also raises the oxygen level, which, when combined with existing hydrocarbons, can create a flammable mixture if not properly managed.

What are the three stages an atmosphere in a cargo tank goes through during purging?

The three stages are: 1) Too rich, where hydrocarbons are too much and cannot catch fire; 2) Flammable range, where the hydrocarbon percentage is just right to cause a fire or explosion with a heat source; 3) Too lean, where hydrocarbons are so low that a flammable atmosphere does not form.

What is the 'lean level' referred to in the context of purging a cargo tank?

The 'lean level' is when the hydrocarbon percentage in a cargo tank is so low that introducing oxygen will not create a flammable atmosphere, thus preventing fire or explosion.

What are the three methods used to purge hydrocarbons from a cargo tank?

The three methods are: 1) Displacement method, 2) Dilution method, and 3) Positive displacement method. Each method aims to expel the existing atmosphere in the cargo tank.

Why is inert gas considered safe for introducing into a cargo tank?

Inert gas is considered safe because it lacks both the hydrocarbon fuel and oxygen, preventing the atmosphere inside the cargo tank from becoming flammable.

What is the target hydrocarbon level in a cargo tank before introducing fresh air, according to the script?

The target hydrocarbon level should be below two percent by volume to ensure that introducing fresh air will not make the atmosphere inside the cargo tank flammable.

What is the final step in making a cargo tank safe for gas freeing, as described in the script?

The final step is to confirm with gas detectors that the hydrocarbon level is below two percent by volume and that the inert gas has less than five percent oxygen before introducing fresh air into the cargo tank.

Outlines

00:00

🚢 Understanding Cargo Tank Purging

This paragraph explains the dangers of the atmosphere inside a cargo tank on an oil tanker, which can contain lethal gases like hydrogen sulfide and hydrocarbons. It discusses the process of purging, which involves introducing inert gas to expel these dangerous gases. The main goals of purging are to reduce hydrogen sulfide levels to non-dangerous levels and to make the tank gas-free by reducing hydrocarbon percentages. The paragraph also explains why fresh air cannot be introduced directly into a cargo tank without first purging it of hydrocarbons, as the presence of oxygen could lead to an explosion if a source of ignition is present. The three stages of purging a cargo tank are described: when the atmosphere is too rich, in the flammable range, and too lean. The goal is to reach a lean level where the hydrocarbons are below 2%, making it safe to introduce fresh air and proceed with gas freeing.

05:00

🔍 Safely Introducing Fresh Air into Cargo Tanks

This paragraph emphasizes the importance of ensuring that the hydrocarbon level in a cargo tank is below 2% before introducing fresh air. It explains that once this level is confirmed by gas detectors, it is safe to proceed with gas freeing. The paragraph concludes with a reminder of the main purpose of purging hydrocarbons from a cargo tank, which is to avoid the flammable range. The speaker encourages viewers to share, subscribe, and like the video if they found it informative, and ends with well-wishes for the viewers' safety and learning.

Keywords

💡Hydrogen Sulfide

Hydrogen sulfide is a colorless gas with a characteristic rotten egg smell. It is highly toxic and flammable, making it dangerous to human life and a potential hazard on oil tankers. In the context of the video, it is one of the gases that need to be purged from cargo tanks to ensure a safe working environment. The script mentions that 'the atmosphere inside a cargo tank can contain hydrogen sulfide which is obviously a dangerous gas for any human being.'

💡Hydrocarbons

Hydrocarbons are organic compounds consisting entirely of hydrogen and carbon atoms. They are commonly found in petroleum and natural gas and can be explosive when mixed with air and ignited. The video discusses the importance of reducing hydrocarbon levels in cargo tanks to prevent explosions, stating that 'it can contain hydrocarbons that are not just dangerous for a human being if inhaled, but they can also lead to an explosion.'

💡Perching Purging

Perching purging is a procedure used on oil tankers to remove dangerous gases from cargo tanks by introducing an inert gas. This process is crucial for making the tanks safe for entry or further operations. The script explains that 'to get rid of all of these gases that are inside the cargo tanks the normal procedure that is adopted on an oil tanker is called as perching purging.'

💡Inert Gas

An inert gas is a substance that does not react chemically with other substances under normal conditions. In the context of the video, inert gas is used to purge cargo tanks of dangerous gases like hydrogen sulfide and hydrocarbons. The script mentions that 'you are introducing the inert gas into a cargo tank for the purpose of expelling the atmosphere inside a cargo tank out.'

💡Flammable Range

The flammable range, also known as the explosive limits, is the range of concentrations of a flammable gas or vapor in air within which combustion will occur upon exposure to an ignition source. The video emphasizes the importance of keeping the hydrocarbon levels below this range to prevent fires or explosions, as indicated by 'the only thing that is remaining to complete the fire triangle and cause an explosion or fire is the fire spark or any source of heat or ignition.'

💡Gas Freeing

Gas freeing is the process of making a confined space safe for entry by removing all dangerous gases. In the context of the video, it is the final step after purging to ensure that the cargo tank is safe for workers. The script states that 'once the flammable atmosphere is not going to form it's not going to catch fire or cause an explosion in case a source of heat or ignition is introduced... then you can actually start gas freeing a cargo tank.'

💡Displacement Method

The displacement method is one of the techniques used to purge hydrocarbons from cargo tanks. It involves pushing the hydrocarbons out of the tank by introducing a different gas, such as inert gas. The video mentions this as one of the 'three methods that are adopted to purge the hydrocarbon from a cargo tank.'

💡Dilution Method

The dilution method is another purging technique where the concentration of hydrocarbons in the tank is reduced by mixing it with a large volume of inert gas, thereby reducing the risk of explosion. The script refers to this method as one of the ways to 'expel the atmosphere that is already in a cargo tank.'

💡Positive Displacement Method

The positive displacement method is a purging technique that uses a mechanical device to force the inert gas into the tank, pushing out the existing atmosphere. This method is highlighted in the video as a way to 'expel the atmosphere that is already in a cargo tank.'

💡HC Detector

An HC detector, or hydrocarbon detector, is a device used to measure the concentration of hydrocarbons in the air. It is crucial for determining when a cargo tank is safe for entry or other operations. The video script emphasizes the importance of using an HC detector to ensure that 'the inert gas that is going inside a cargo tank has an oxygen that is less than five percent.'

Highlights

The atmosphere inside a cargo tank on an oil tanker can be lethal and dangerous due to the presence of gases like hydrogen sulfide and hydrocarbons.

Perching purging is a procedure used to remove dangerous gases from cargo tanks by introducing inert gas.

The primary purposes of purging are to expel hydrogen sulfide and hydrocarbons to make the atmosphere safe for human life and prevent explosions.

Introducing fresh air into a cargo tank can be risky because it raises the oxygen level, which combined with hydrocarbons can lead to an explosion.

Punching a cargo tank is necessary before purging to reduce the hydrocarbon levels to avoid creating a flammable atmosphere.

A flammable atmosphere in a cargo tank is defined as the presence of a correct percentage of hydrocarbons that can ignite with a source of heat.

The atmosphere in a cargo tank goes through three stages during purging: too rich, flammable range, and too lean.

The goal of purging is to reach a lean level where the hydrocarbons are below 2% to prevent fire or explosion even with a heat source.

There are three methods to purge hydrocarbons from a cargo tank: displacement, dilution, and positive displacement.

Inert gas used in purging lacks both fuel (hydrocarbons) and oxygen, preventing the atmosphere from becoming flammable.

A flammability diagram is used to ensure that hydrocarbon levels are reduced below 2% to avoid trouble when introducing fresh air.

A good hydrocarbon (HC) detector is essential to measure the atmosphere inside a cargo tank and confirm the inert gas has less than 5% oxygen.

Once the hydrocarbon level is confirmed to be below 2%, it is safe to introduce fresh air and begin gas freeing the cargo tank.

The main purpose of purging hydrocarbons is to avoid the flammable range, ensuring safe gas freeing operations.

The video concludes with a reminder to stay safe and continue learning about the safety procedures on oil tankers.

Transcripts

hello and welcome back to my time genie

all of you people who are already

serving on the oil tankers they already

know that the atmosphere inside a cargo

tank is not only lethal for a human life

it can also be dangerous for your ship

more specifically the atmosphere inside

a cargo tank can contain hydrogen

sulfide which is obviously a dangerous

gas for any human being

it can contain hydrocarbons that is not

just dangerous for a human being if

inhaled

but it can also lead to an explosion

to get rid of all of these gases that

are inside the cargo tanks the normal

procedure that is adopted on an oil

tanker is called as perching purging

simply means that you are introducing

the inert gas into a cargo tank

for the purpose of expelling the

atmosphere inside a cargo tank out

and the two main purposes for which the

purging is done is to expel the hydrogen

sulfide

from a cargo tank and also the

hydrocarbons from a cargo tank the

hydrogen sulfide is purged from the

cargo tank for obvious reasons the main

purpose is to reduce the hydrogen

sulfide level in a cargo tank to such a

level

that is not dangerous to human life

anymore in case

it escapes on the main deck and the

hydrocarbon percentage in a cargo tank

is reduced before the tank is made

gas free now you may be asking yourself

why is it required to punch a cargo tank

before caspering i mean in any case

if we introduce the fresh air into a

cargo tank it will expel

all the atmosphere of a cargo tank out

right wrong it is true that once you

introduce the fresh air into a cargo

tank

once you push the fresh air into a cargo

tank obviously it will expel the

atmosphere of the cargo tank out

but there is another thing and that is

when the fresh air goes inside a cargo

tank the oxygen in the cargo tank is

obviously

raised because the fresh air when it's

coming

from the fresh atmosphere outside it is

bringing the oxygen that is 20.9 percent

into a cargo tank

now inside a cargo tank there is already

hydrocarbons so

the fuel is there the oxygen is there

now the only thing that is remaining to

complete the fire triangle and cause an

explosion or

fire is the fire spark or any source of

heat or ignition so just as a precaution

and before the introduction of the fresh

air in a cargo tank

the atmosphere of the cargo tank is

basically purged out of the hydrocarbons

the hydrocarbons on a cargo tank are

reduced to such a level

that when they are mixed with 20.9

percent of oxygen the atmosphere of a

tank does not

go into a flammable range now you might

be asking yourself

what is a flammable range and how are we

going to know about it usually the

atmosphere of a cargo tank goes through

three stages when you are purging a

cargo tank the first stage is obviously

when the atmosphere is too rich

it basically means that the hydrocarbons

inside a cargo tank are too

much the atmosphere is so rich that it

cannot catch fire

the second stage would be when the

atmosphere is in a flammable range

it means that once a source of heat or

ignition is introduced in a cargo tank

the percentage of hydrocarbons in a

cargo tank is

just right to cause a fire or explosion

and the third stage is when the

atmosphere is too

lean too lean means that the percentage

of hydrocarbons in a cargo tank is

so less that if you introduce the oxygen

into a cargo tank the flammable

atmosphere is not going to form

and once the flammable atmosphere is not

going to form it's not going to catch

fire or cause an explosion in case a

source of heat

or ignition is introduced now our main

purpose when we are purging a cargo tank

is to reach

this lean level we want to reduce the

hydrocarbons to such an extent

that in case the source of heat or

ignition is introduced in a cargo tank

it does not catch fire

there are usually three methods that are

adopted to purge the hydrocarbon from a

cargo tank the first is

displacement method the second is

dilution method and the third is

positive displacement method all of them

are basically done in a little different

way

but the basic purpose is exactly the

same that is to expel the atmosphere

that is already in a cargo tank

now you might ask that if you are

reproducing the inert gas into a cargo

tank then

how is the inert gas safe basically

these are the gases that are produced

after burning the fuel that means that

they do not only lack

the fuel itself the hydrocarbon itself

but it also lacks in

oxygen and thus it prevents the

atmosphere that is inside a cargo tank

to fall into that flammability range

if you see this flammability diagram

then basically the basic purpose of all

of this operation

is to bring the hydrocarbon to below two

percent of hc

if the hc in a cargo tank are above two

percent and you introduce the fresh air

inside a cargo tank

then basically you are inviting a

trouble for yourself by making the

atmosphere inside a cargo tank

flammable

so you have to use a good hc detector

not to just measure the atmosphere

inside a cargo tank

but also to measure that the inert gas

that is going inside a cargo tank

has an oxygen that is less than five

percent once the atmosphere in a cargo

tank is achieved

that is it is below two percent by

volume of

hc once it is confirmed by your gas

detectors that it is actually so

it is safe to introduce fresh air inside

a cargo tank and then

you can actually start gas freeing a

cargo tank so all in all the basic

purpose of purging the hydrocarbons from

a cargo tank is basically

to avoid flammable range that's the main

purpose

once the desired hydrocarbon travel is

reached that is less than two percent by

volume

it is safe to introduce fresh air inside

a cargo tank and this way

we can carry out the gas spring

operation of a cargo tank

safely that's all for today i hope you

have learned something out of it if you

did

consider sharing consider subscribing

and consider liking this video stay

happy

stay safe stay well and happy learning