There are two types of gas detection systems used throughout the ship covering all the cargo, machinery and accommodation spaces. The systems use the infrared gas analyser method and the catalytic combustion method.
The two systems are:
- BH19 Tank-Scan Aspirated System
The system is situated in the electrical equipment room and the sampling sequence is automatically controlled by solenoid selection valves, with the sampled gas being drawn into the panel by pumps, before passed over an infrared gas analyser.
The system draws samples from the following locations:
- Cargo hold spaces – upper and lower
- Cargo tank annular spaces – upper and lower
- Vent masts – 4 sets
- Double bottom pipe passage – forward and aft
- Under deck passages – port forward and aft, starboard forward and aft
- Cargo compressor room – upper and lower
- Cargo motor room
The analyser works on the principle that infrared light is absorbed by the methane gas. Methane gas has a distinctive absorption band in the infrared spectrum. Therefore if a sample of gas is compared against a reference sample of air, the difference in output from an infrared sensor will be in proportion to the gas concentration.
If the methane concentration of any sample point reaches 30% LEL, an audible alarm is sounded and the corresponding indicator lamp is lit on the panel. Additionally, a gas detection alarm is activated on the DCS graphic screen T30-429-01 CARGO GAS DETECTION and on the extension alarm panel in the fire control station. The system also contains an internal gas sensor to detect the flammable gas level inside the panel. The unit will shut off the power supply if an internal gas leak is
- TQ 800 System
The system contains of groups of 4-20mA Measurement Cards, each measuring a single detector and displaying the reading on the front of the card. They monitor the atmosphere continuously at the points where sensing heads are fitted and will detect the presence of any combustible gas should it accumulate. The sensors provide electrical outputs to the cards, proportional to the amount of gas present, to alarm and indicating panels.
The front panel of the Measurement Cards display pushbuttons and indicator
LEDs as follows:
- SEL – select button
- SPR – Special function button
Graphic – T30-429-01