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Gas measuring instruments test and calibration procedure
Gas detection equipment is required for ensuring spaces are safe for entry, work or other operations. Their uses include the detection of:
All vessels are supplied with portable gas measuring equipment, according to the specific requirements of the vessel owners.
Personnel must fully understand the purpose and limitations of vapour detection equipment, whether fixed or portable.
- Cargo vapour in air, inert gas or the vapour of another cargo.
- Concentrations of gas in or near the flammable range.
- Concentrations of oxygen in inert gas, cargo vapour or enclosed spaces.
- Toxic gases
The importance of careful calibration cannot be over emphasised as the gas detection or analysing equipment will only give accurate readings
if calibration is carried out strictly in compliance with the manufacturer’s instructions and using the correct calibration gases.
Instruments must always be checked, zeroed and spanned where applicable before every use as per the manufacturer’s instructions.
Calibration may be required to be carried out ashore for some instruments. The Chief Officer is responsible for the
condition monitoring and maintenance of all portable and fixed gas measuring instruments on board and ensuring sufficient span gas of the
correct grade is on board.
The Chief Officer is responsible for identifying, calibrating, and adjusting all portable gas measuring instruments available onboard.
- For all Meters on board the Manufacturer’s Operating Manual and a suitable Calibration Kit must be on board.
- The performance of these meters is to be scrupulously monitored and repairs arranged in the case of malfunction.
- These meters are a high cost item and must be looked after carefully. If supplied with carrying cases and or covers they should be used at all times.
- Meters may be combined in one instrument i.e. combined 02 meter and explosimeter.
- Toxic gas tubes have a limited shelf life
Operational checking and calibration
The difference between operational checking (zero & spanning) of an instrument and calibration should be clearly understood:
- Checking an instrument involves spanning and zeroing the instruments using the calibration gas of known gas content to ensure the gas readings are within manufacturer’s stated tolerances.
- If the instrument readings are out of tolerance, than the meter will have to be calibrated. Calibration involves applying the calibration gas of known gas content to the instrument and then adjusting the sensor output control to read the same as the known gas content.
Gas testing equipments should be tested and if necessary re-calibrated monthly. The results of the test should be recorded in the planned maintenance system.
A full history of each instrument should be kept, including:
- Meter description and serial number.
- Date last calibrated onboard.
- Date last serviced ashore.
- Date next shore service due.
Instruments carried onboard
Due to the requirements of the various ship owners, the exact type of instrument will vary from ship to ship.
Each vessel will however carry instruments capable of measuring Oxygen, Hydrogen Sulphide, Methane, Carbon Monoxide,
Carbon Dioxide and also the lower explosive limit.
Combined function meters
There are certain instruments which have a combination of functions. Examples of some types of equipment which may be carried are:
Riken RX415 : this instrument measures and monitors CH4 and O2
Riken RX515 : this instrument measures and monitors CH4, O2, CO2 and
Personal monitoring meters
Some instruments can be carried in a pocket such as a Personal Oxygen Meter, used for entry into enclosed spaces. Such instruments are intended only as a personal monitor and will give an audible and visual alarm if the Oxygen content falls below its preset level.
As monitors, they are NOT designed for testing the atmosphere for oxygen or other gases. Care must be taken to ensure that they are therefore not used for testing.
Draeger PAC5000 : this instrument measures O2, CO and H2S
Riken GX2001 : this instrument measures LEL, O2, H2S and CO
Toxic gas detectors
These detectors measure relatively low concentrations of toxic gases. Such gases may include Carbon Monoxide or Hydrogen Sulphide.
The type of instrument will normally require a special attachment or tube which the gas is aspirated through. It is necessary to know in advance what gas is expected in order to choose the correct detection tube. The readings are to be compared with the occupational exposure limits or threshold value limits.
The material and condition of sample lines can affect the accuracy of gas measurements. Sample tubing which is cracked or blocked or which has become contaminated with oil or other substances may seriously affect instrument readings.
The tubing must always be checked before and during use and if necessary be cleaned or replaced.
It is also important to realise the length of tubing and compare to the meter manufacturer’s instructions as to the number of aspirations per metre length. If this is not done there is a danger that the sample gas may not reach the meter sensor and therefore give a false reading.
Supply ,service and maintenance procedures
All new meters and all meters returned following shore servicing and calibration should be fully certified.
Below is our guideline for handling LNG cargo:
- Preparation for loading LNG
- Procedures for LNG cargo loading
- Procedures for LNG cargo discharging
- How LNG transferred from shore to ships cargo tanks ?
LNG vessel cargo handling equipment
- LNG vessel cargo piping system
- Precautions for LNG carrier during loaded passage
- Precautions for LNG carrier during ballast passage
- Drydocking preparations for LNG vessel
- LNG spill risk during marine transportation
- Risk of sloshing effect on LNG cargo tanks
- Liquefied gas carrier safety training
- Inert Gas Hazards and Precautions -
Atmosphere Control For Gas Carrier
- Stability and cargo loading limitations - use of loading computer
- How to avoid structural steels suffering brittle fracture at low temperatures ?
- How to tackle LNG fire ? Available fire fighting agents & safety aspects
External links :
The Center for Liquefied Natural Gas : ( CLNG ) - A trade association of LNG producers, shippers, terminal operators and developers, energy trade associations and natural gas consumers
- Liquefied Gas Handling Principles on Ships and in Terminals
- International Safety Guide for Oil Tankers and Terminals
- International Code for the Construction and Equipment of Ships carrying Liquefied Gases in
- Code for the existing ships carrying Liquefied Gases in Bulk 1976 with Amendments and
- Code of Safe Working Practices
- International Convention for the Safety of Life at Sea
- International Convention on Standards of Training, Certification and Watch keeping for
- SIGTTO Liquefied Gas Handling Principles On Ships And In Terminals
- Shipboard Oil Pollution Emergency Plan
- USCG Non-Tank Vessel Response Plan
- LNG vessel cargo containment system
LNG spill risk during marine transportation and hazards associated
- How to tackle fire on board LNG ship
- Fire fighting plan for LNG cargo
- Increased Cargo Capacity for LNG ships & Advantages of the dual fuel diesel electric propulsion
LNG operating instructions- various important terms related with cargo handling
The sea transport of liquefied gases in bulk -Where do the products come from ?
LNG vessel construction - advantages of membrane technology
Advantages of Moss rosenberg cargo containment system
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