Inert gas system safeties: In November 2012, five officers on board an LPG tanker passed away from asphyxiation as a result of their “disassembly” of a spectacle blind—also referred to as a spectacle flange or figure-8 blind—without turning off the inert gas supply.
According to the investigation report, while removing the spectacle blind, six officers on board the LPG carrier failed to turn off the inert gas supply and make sure there was no inert gas in the pipe. This resulted in the release of inert gas into the compressor room, which caused asphyxiation.
The inert gas (IG) system is a crucial component of tanker ship cargo operations, and it must be managed carefully because inert gas can be harmful to people.
To protect themselves while working on ships, officers using the IG system need to take some safety measures.
The significance of inert gas on board
One essential device for onboard protection against explosion is an inert gas system. Specifically, aboard ships that regularly transport hazardous cargo—explosive or flammable materials being among the most dangerous—inert gas systems are indispensable. This crucial integrated system can be used as a stand-alone inert gas plant or to process ship boiler flue gas. While inert gas systems are optional for dry cargo ships, SOLAS, and more especially Fire Safety Code chapter 15, require them for oil and chemical tankers.
Risks to one’s health when breathing inert gas
Oxygen shortage and health risks from combustion gases, carbon monoxide (CO), and sulfur dioxide (SO2) are the health risks associated with flue and inert gases. Inhaling the inert gas can result in respiratory difficulties, neurological disorders, oxygen shortages, and, if left untreated, even death.
The gas carbon monoxide (CO) has no flavor or color and no warning signs when inhaled. Inhalation can be lethal and cause depression of the central nervous system. At greater concentrations, sulfur dioxide (SO2), a harsh, sulfurous-smelling gas, can irritate the eyes and respiratory system. Chest discomfort, extreme breathing difficulties, and even death may result from inhalation. Remove the person from the contaminated area, give them oxygen, and perform CPR if needed if they have ingested CO or SO2. In any event, get medical help or guidance as soon as you can.
10 Precautions in Handling Inert Gas System safeties
1. Ensure that inert gas safety devices are properly maintained
The purpose of safety devices on IG systems is to stop cargo gasses from leaking back into the machinery spaces. For further safety, a water seal and a vent must be installed on the main deck in addition to the non-return valve.
At times, the scrubber’s bottom is equipped with an extra water seal. These gadgets must be always kept up to date.
2. Verify Sufficient Oxygen Level
The human body is highly vulnerable to oxygen shortage. It can easily result in death in addition to brain damage.
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When there is an oxygen shortage, the mind tends to become indifferent and complacent. If escape is tried at this point, physical exertion will exacerbate the body’s and mind’s weakness.
Because of this, it’s imperative to fully ventilate the cargo tanks in order to guarantee that there are no residual pockets of oxygen deprivation and that a consistent 21% result is always recorded.
3. Verify that no combustible gases are present
It is crucial to remember that hydrocarbon gases are particularly harmful because they are combustible and the inert gas has no effect on their toxicity.
To get rid of any potential gas pockets, tanks must be properly gas freed. Using a trustworthy combustible gas indicator, any given compartment must provide a reading of zero or 1% of the lower flammable limit (LFL).
4. Eliminate Hazardous Elements from Flue Gases
The amount of flue gases in the tank should be measured using an authorized combustible gas indicator. During the gas liberating process, the levels of nitrogen, carbon monoxide, and sulfur dioxide found in flue gases must be accurately assessed.
Following ventilation, the tank’s flue gas reading should be 1% or less than the LFL and its oxygen measurement should be 21%. Before entering, ventilation should be maintained until a consistent reading of 21% oxygen is obtained.
5. Verify the pressure in the tank
Prior to opening any tank lids, ullage plugs, or apertures for tank washing, make sure the tanker pressure is checked. Before opening any tanks, the pressure in inerted cargo tanks must be sufficiently lowered.
6. Stop Air From Getting Into the System
Action must be done right once to stop air from being sucked into the cargo tanks in the event that an inert gas system is unable to supply the necessary amount and quality of inert gas or is unable to maintain a positive pressure in the tanks.
The inert gas deck isolating valve must be closed, the vent valve between it and the gas pressure regulating valve (if available) must be opened, and all cargo and ballast discharge from inerted tanks must be stopped. Other urgent repairs to the inert gas system must also be made.
7. Implement Strategies to Avoid Electrostatic Ignition
Hydrocarbons in the tanks have the potential to be hazardous. When the oxygen content of the tank rises as a result of air inflow, there is a chance of an electrostatic fire if the environment of the tank contains flue gas, which contains tiny particulate matter with a minor electrostatic charge.
Stop air from entering the tanks in any way.
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8. Before doing any repairs, gas freeing
Even if inert gas leaks into the open, it can quickly cause hypoxia and render a person unconscious.
Therefore, extra attention must be used when doing any maintenance or repairs on the IG plant.
It is advised that before beginning any work, the I.G. plant be totally gas released. Any unit in the I.G. system should only undergo internal inspection after the usual operating procedures for entering enclosed spaces have been completed.
9. Watch out for hydrogen sulfide
In tankers, particularly those transporting sour crude oil, pyrophoric deposits occur when the oxygen concentration is lowered during I.G. system operation.
These deposits combine with petroleum to generate extremely poisonous hydrogen sulfide. If they are not appropriately eliminated, pyrophors and hydrogen sulfide that are created during a laden transit may continue to exist throughout subsequent ballast passages.
10. Ensure Blowers Are Operating Properly
Blowers are typically used to liberate gases from oil tankers; therefore, an air inlet (suction from the atmosphere) at the blower’s suction side with a blanking mechanism must be provided.
The blanking setup needs to be secured for proper operation. It must be opened during gas freeing, and the blower must supply the tanks with air.
