Why Hazardous Area Exist
An LNG carrier continuously transports cargo at approximately -163°C.
Under normal operating conditions, the cargo containment system remains completely closed.
However, every cargo operation involves potential gas release points:
- Cargo manifolds
- Cargo valves
- Pipe flanges
- Vent risers
- Pressure relief valves
- Compressor rooms
Instead of assuming gas will never escape, LNG carrier designers take the opposite approach.
They assume gas release is possible and design the vessel accordingly.
This philosophy is the foundation of hazardous area classification.
A Different Way to Think About Hazardous Areas
One of the best explanations I ever received was surprisingly simple.
Imagine invisible gas clouds surrounding every potential release point.
The closer you are to that source,
the greater the probability of an explosive atmosphere.
That is exactly how Zone 0, Zone 1 and Zone 2 are defined.
They are not arbitrary circles drawn on drawings.
They represent different probabilities of gas presence
Zone 0: Gas Is Expected to Be Present
Zone 0 is the most hazardous classification.
An explosive gas atmosphere exists continuously or for long periods.
Typical examples include:
- Cargo tanks
- Vapour spaces
- Cargo piping
- Pressure relief piping
No ordinary electrical equipment can be installed here.
Everything must be specially designed for explosive atmospheres.
Fortunately, crew members rarely enter these spaces during normal operations.
Zone 1: Gas May Be Present During Normal Operations
Most deck officers and cargo engineers become very familiar with Zone 1.
Typical Zone 1 locations include:
- Cargo manifolds
- Cargo valves
- Pipe flanges
- Compressor room entrances
- Cargo tank domes
- Areas within approximately 3 meters of cargo openings
Normal cargo operations may release small quantities of gas.
Therefore, ignition sources must be strictly controlled.
Portable radios,
flashlights,
gas detectors,
and electrical equipment
must all be certified for hazardous area use.
Zone 2: Lower Probability Does Not Mean No Risk
Many junior officers mistakenly assume Zone 2 is a “safe area.”
It is not.
Zone 2 simply means that explosive gas atmospheres are not expected during normal operations and, if they occur, they should exist only briefly.
These areas often surround Zone 1 boundaries and spill containment spaces.
During abnormal situations, Zone 2 can quickly become hazardous.
For this reason, inspectors continue paying close attention to these locations.
Looking at the Hazardous Area Plan
(Insert the hazardous area drawing here.)
One interesting observation becomes immediately apparent.
The cargo tank itself is not the only hazardous area.
The gas release sources create invisible protection zones extending throughout the deck.
Notice the large cylinders surrounding the cargo vent masts.
These represent areas where significant volumes of vapour may be released during:
- Cargo loading
- Cargo discharge
- Ballasting
- Pressure relief operations
This explains why accommodation air intakes are located far away from these vent outlets.
It is a design philosophy rather than simply a regulatory requirement.
Why Accommodation Openings Are Located So Far Away
Many cadets ask why accommodation doors and ventilation intakes are positioned toward the aft side of the accommodation block.
The answer becomes obvious once hazardous areas are understood.
If cargo vapour enters the accommodation ventilation system,
the consequences could be extremely serious.
For this reason, the IGC Code requires separation distances between:
- Cargo vent outlets
- Air intakes
- Accommodation openings
- Control stations
The objective is simple.
Keep gas outside and people inside safe.
An Engineer’s Perspective
After years onboard LNG carriers, I rarely think about hazardous areas as coloured drawings.
Instead, I naturally ask different questions.
Is this portable light certified?
Can this maintenance work be performed here?
Is the ventilation operating correctly?
Why is this compressor room designated as Zone 1?
The drawing becomes part of everyday operational decision making.
What Surveyors Usually Notice
One interesting trend in modern inspections is that surveyors increasingly verify whether crew members actually understand hazardous area classification.
Typical questions may include:
“Why can’t you use an ordinary grinder here?”
“What type of portable radio is permitted?”
“Why is this ventilation fan Ex-certified?”
The objective is not to test memory.
It is to confirm that crew members understand the relationship between gas release and ignition sources.
A Lesson I Learned Onboard
One thing I appreciate about LNG carriers is that almost every design decision has a clear engineering reason.
Hazardous area classification is no exception.
The coloured circles on a drawing may initially appear complicated.
In reality, they represent decades of experience, accident investigation, and engineering improvements.
Understanding those invisible boundaries changes the way engineers, officers, and surveyors look at the ship.
And perhaps that is the most important lesson.
Hazardous areas are not simply regulatory zones.
They are carefully designed safety margins that allow thousands of tonnes of LNG to be transported safely across the world every single day.
