Waterfront Shipping Company Limited
Hazards of a Nitrogen Generation Plant
Onboard a Ship
- What you need to know to be safe -
Nitrogen (N2)
The Silent Killer….
*Film footage courtesy of BP
Nitrogen (N2)
First, the good news:
Nitrogen is part of the life cycle
and, as humans, we need some
nitrogen to stay alive – PROVIDED
we get it in the right quantities.
Breathable air consists of 21%
oxygen, 79% nitrogen with some
other trace amounts of assorted
Nitrogen (N2)
It is a naturally occurring part of the atmosphere and comprises
approximately 79% of the air that we breathe.
It is essential to life as it forms a constituent part of the human DNA
and as such, forms part of our genetic code.
Nitrogen is a colourless, odourless and tasteless gas.
Nitrogen (N2)
Nitrogen (N2)
Next, the bad news:
Every year people die in nitrogen-rich / oxygen-deficient
atmospheres because of ignorance, attitude and a failure to
adhere to safe work practices.
It can and will kill you if you get it wrong.
Nitrogen will surprise you only once –
Within the last 5 years for example, BP has experienced 24
incidents involving nitrogen that resulted in 5 fatalities.
Nitrogen (N2)
IMO through SOLAS mandates that chemical tankers with cargo
tanks in excess of 3,000 M3 must have their tanks inerted.
Ships with cargo tanks under 3,000 M3 are not required to inert the
tanks at this time, but may be required to do so depending on the
cargo they are carrying and the terminals at which they will be
Due to past incidents, IMO is now looking at the possibility for all new
and existing chemical ships under 20,000 mts dwt to have inert gas
systems onboard.
Filling the cargo tanks and associated piping systems with a gas or
vapour that will reduce the oxygen content to 8% or below and will
not support combustion nor react with the cargo and will maintain
that condition.
Legal and Maintenance
SOLAS requires the installation of devices that will not allow the
reverse flow of inert gas back into the machinery spaces.
These devices may be either a deck water seal, or a block valve in
the inert gas line of any inert gas system.
The regular maintenance of these items is to be adhered to
rigorously in order to prevent the flow of inert gas back into the
machinery spaces.
When performing maintenance on the N2 plant it is equally important
to ensure that the plant is totally gas-free before work commences.
Nitrogen – Flammability
As an inert gas, nitrogen does not support combustion. It is
this property that makes it ideal for use on ships that require
inert atmospheres in their cargo tanks to eliminate any chance
of fire and/or explosion.
The National Fire Protection Association (NFPA) has assigned
a flammability rating to nitrogen of ‘zero’ (0), in other words, it
is not combustible – it will not burn.
In addition, it is deemed to be a “clean” gas that will not
contaminate or interact with the cargo.
Nitrogen – Tank Entry
Tank Entry Hazards and Awareness
Nitrogen – Tank Entry
Nitrogen is slightly lighter than air at ambient temperature, so it will
tend to rise towards the upper levels in a space.
You need to be aware of this should you ever need to open the
main access hatches (or any tank opening) of the cargo tanks
when they are full of cargo and the ullage space above the cargo
contains nitrogen.
It is possible that some of the N2 could
move up and out of the hatch access
and if you are in the way …… !!!
So, do a risk assessment
Nitrogen – Tank Entry
Wear the appropriate PPE and a gas detection sensor at all times
and follow procedure by using a checklist.
When an inerted tank is maintained at a positive pressure,
personnel should be aware of some additional hazards.
For example, this pressure must be adequately reduced before
opening any access to the tanks, such as the main access hatches,
ullage ports and tank washing hatches.
Nitrogen – Tank Entry
Can you see or
smell the invisible killer?... No!
• How do you know the tank is safe to
• Have you completed a checklist?
• What precautions do you take
before entry?
• Do you have a portable gas detector
that will ‘beep’ if the O2 level falls
below 19%?
• Do you have a man on stand-by at
the tank access hatch?
• Do you know that you can be
overcome by N2 just by looking into
the open tank access hatch without
wearing breathing apparatus?
Nitrogen – Tank Entry
Check, check, check!!!!
Nitrogen – Physiological Effects
Physiological Effects – Oxygen Deficiency
% Oxygen
Effects & symptoms
Maximum ‘safe level’ (23.5% is often the high level alarm setting on most O 2
Typical O2 concentration in breathable air
Minimum ‘safe level’ (19% is often the low level setting on most O2 detectors)
First signs of hypoxia. Decreased ability for strenuous work. May induce early
symptoms in persons with coronary, pulmonary or circulatory problems
Respiration increases with exertion, pulse rate increases, impaired muscular
coordination, perception & judgement
Respiration further increases in rate and depth, poor judgement, lips turn blue
Mental failure, fainting, unconsciousness, ashen face, blueness of lips, nausea,
vomiting, inability to move freely
6 minutes exposure – 50% probability of death
8 minutes exposure – 100% probability of death
Coma in 40 seconds, convulsions, respiration ceases, death
Nitrogen – Physiological Effects
What happens when you breathe in nitrogen?
The brain becomes starved of oxygen
 You pass out in approximately 10 to 12 seconds
 The brain shuts down
 It only takes ONE BREATH
What if I hold my breath?
Holding your breath causes the oxygen in your blood to be used up.
If you then inhale the inert atmosphere (N2), suffocation and death
will follow in most cases.
Physiological Effects  Death by Nitrogen
Exposure to an atmosphere with a low concentration of oxygen (O2)
does not necessarily produce any recognizable symptoms before
unconsciousness occurs.
The onset of brain damage and death can follow in as little as 2 to 4
If oxygen deficiency is not sufficient to cause unconsciousness, the
mind nevertheless is liable to become apathetic and complacent.
Even if the victim notices these symptoms and attempts to escape,
the physical exertion will just aggravate the weakness of both mind
and body to the extent that escape is probably not going to happen.
Ugly news !
Nitrogen is listed a a natural asphyxiant. In other words, in areas where N2
is abundant and the level of O2 is insufficient to support life, nitrogen will
block the body’s autonomous response to inhalation. Basically, you are
not able to breathe in and……………….
Remember that…
I am…
I am…
I have no…
I am a…
You do not want to meet this fellow
Thank you to BP for the use of their material.