What are regulations for quantity of Carbon dioxide used as Fire Extinguisher onboard as per SOLAS or FSS Code ?

Regulations for Quantity of fire-extinguishing medium are:

1. For cargo spaces the quantity of carbon dioxide available shall, unless otherwise provided, be sufficient to give a minimum volume of free gas equal to 30% of the gross volume of the largest cargo space to be protected in the ship.
2. For machinery spaces the quantity of carbon dioxide carried shall be sufficient to give a minimum volume of free gas equal to the larger of the following volumes, either:
   • 40% of the gross volume of the largest machinery space so protected, the volume to exclude that part of the casing above the level at which the horizontal area of the casing is 40% or less of the horizontal area of the space concerned taken midway between the tank top and the lowest part of the casing; or
   • 35% of the gross volume of the largest machinery space protected, including the casing.
   • The percentages specified in paragraph above may be reduced to 35% and 30%, respectively, for cargo ships of less than 2,000 gross tonnage provided that, where two or more machinery spaces are not entirely separate, they shall be considered as forming one space.
3. For the purpose of  above paragraph the volume of free carbon dioxide shall be calculated at 0.56 m3/kg.
4. For machinery spaces, the fixed piping system shall be such that 85% of the gas can be discharged into the space within 2 min.

You may also know regulations for control of CO2 system

Carbon dioxide systems shall comply with the following requirements:

1. Two separate controls shall be provided for releasing carbon dioxide into a protected space and to ensure the activation of the alarm. One control shall be used for opening the valve of the piping which conveys the gas into the protected space and a second control shall be used to discharge the gas from its storage containers; and

2. The two controls shall be located inside a release box clearly identified for the particular space. If the box containing the controls is to be locked, a key to the box shall be in a break glass- type enclosure conspicuously located adjacent to the box.