How the requirement of co2 in a ship is calculated? How is the number of bottles of co2 is calculated?

How the requirement of carbon dioxide in a ship’s installation is calculated. 

Regulation stipulates the requirements of CO2 onboard ships as follows

>For cargo space, 30% of gross volume of largest cargo space

>CO2 of sufficient amount to give minimum value of free gas equal to larger of following volumes
I. 40% of gross volume of largest machinery space excluding casing
II. 35% of gross volume of largest machinery space protected including casing

        Regulation also states that, for machinery space, piping arrangement should be such that 85% of the gas can be discharged into the space protected including the casing with in 2min.
The following information about CO2 is important
Volume of free CO2 should be taken as 0.56m3/Kg (inverse of density)
CO2 content in a bottle is 45.4Kg (standard)Water capacity of the bottle = 65.1 liters (standard)

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For example, consider a ship in which
a. Engine room gross volume (to upper deck) = 4658m3
b. Engine room gross volume to top casing = 5358m3
c. Volume of the largest cargo hold = 6849m3

Calculation of the CO2 cylinder required as per the regulations for the volume of the air reservoir = 375m3
Therefore, for engine room the CO2 bottle requirement is calculated as
For gross volume excluding casing,
(4658+375)*0.4/ (45.4x0.56) = 80 cylinders
For gross volume of engine room including casing,
(5358+375)*0.35/ (45.4*0.56) = 79 cylinders
For cargo hold, requirement is calculated as
(6849*0.30)/(45.4*0.56) = 81 cylinders
The requirement is the largest of the above values, which is 81 cylinders