A gas sampling point on a ship is a fixed, designated location from where atmospheres inside enclosed spaces, tanks, voids, or machinery compartments can be safely tested for gases before entry. It is part of the ship’s safety system and is used to check for oxygen content, flammable gases, and toxic gases without physically opening the space or exposing crew to danger.
Gas sampling points ensure that the atmosphere inside a space is safe for entry, hot work, or maintenance, and they allow continuous or periodic monitoring during operations.
Why Gas Sampling Points Are Needed
Many shipboard spaces can accumulate dangerous atmospheres due to cargo residues, fuel vapours, biological reactions, or lack of ventilation. Gas sampling points eliminate the need to open a tank or hatch to check the atmosphere. Instead, the atmosphere is drawn through dedicated pipes to a safe location where a portable gas detector or fixed system analyzes the air.
This reduces the risk of:
oxygen deficiency
flammable vapour explosions
toxic gas exposure
unexpected release of dangerous fumes during entry
They also support compliance with SOLAS, ISGOTT, SMS, enclosed space entry procedures, and safe working practices.
Where Gas Sampling Points Are Located
Location depends on the type of ship, but common areas include:
Cargo tanks on tankers
Ballast tanks on tankers and bulk carriers
Fuel oil and diesel oil tanks
Void spaces
Forepeak and aft peak tanks
Double bottom tanks
CO₂ room, boiler rooms, and engine room ventilation ducts
Paint stores, chemical lockers, and battery rooms
Cargo holds (on certain vessels)
Sampling points are normally located at a safe, accessible spot outside the tank—often near the tank top, common manifolds, or a designated gas-testing manifold in the pumproom or on deck.
How a Gas Sampling Point Works
A small-diameter sampling pipe runs from inside the tank or space to the ship’s deck or a nearby control point. The inner end of the pipe is positioned in the space to allow representative sampling, usually at multiple heights. The outer end has a quick-connection adapter or hose connection.
To test:
Connect a portable gas detector’s pump hose to the sampling point.
Draw air from inside the tank through the sampling line.
The gas detector analyzes O₂, flammable vapours, and toxic gases.
Record results and determine if the space is safe for entry.
Some ships also have fixed gas detection systems connected directly to sampling points.
Types of Gases Tested Through Sampling Points
Oxygen percentage (to check for deficiency or enrichment)
Hydrocarbon vapours (LEL/UEL)
Toxic gases such as H₂S, CO, SO₂, CH₄ depending on the cargo or operation
A typical test includes:
O₂: Minimum 20.9% for safe entry
Flammable gas: 0% LEL required before enclosed space entry
Toxic gases: Must be within permissible exposure limits
Advantages of Gas Sampling Points
Safer than opening manholes
Allows testing before entry
Helps monitor tank atmosphere during ventilation
Provides representative sampling from difficult-to-reach areas
Reduces risk of sudden release of vapours
Allows compliance with enclosed space entry requirements
Important Safety Points
Always purge the sampling line before taking a reading.
Never assume a tank is safe just because one level tests okay; test multiple levels.
Record readings in enclosed space entry permit.
Check for blockages, corrosion, or moisture in the sampling line.
Use calibrated gas detectors only.
Do not use flames or hot equipment near sampling points, especially on tankers.
