Volume is taken by measuring the extreme beam under the weather deck, (W) the distance from fwd to aft ER bulkheads, (L) and the height from the keelson to the underside of the deck which has an area less than 40% of the largest horizontal area of the machinery space. (H) The volume is then LWH + amount of free air in air receivers. The amount of CO2 is volume (M3) divided by 0.56 (kg/M3) x 0.4 (kg of gas)
from Fire Detection and Extinguishing Equipment Regulations (C.R.C., c. 1422)
http://laws-lois.justice.gc.ca/eng/regu ... html#h-108
SCHEDULE III
FIXED INSTALLATIONS FOR SMOTHERING BY FOAM, GAS, STEAM OR WATER
Smothering Gas
3. (26) Subject to subsections (27) and (29), where CO2 is used as a smothering gas for machinery spaces, the quantity of gas available shall be sufficient to give a minimum quantity of free gas equal to the larger of the following quantities:
(a) 40 per cent of the gross volume of the largest space, the volume to include the casing up to the level at which the horizontal area of the casing is 40 per cent or less of the horizontal area of the space concerned taken midway between the tank top and the lowest part of the casing; or
(b) 35 per cent of the entire volume of the largest space including the casing.
(27) For the purpose of determining the quantity of liquid carbon dioxide required to produce the volume of smothering gas required, 1 kg of liquid carbon dioxide shall be deemed to produce 0.56 m3 of gas.
(28) Subject to subsection (29) where Halon 1301 is used as the smothering gas for machinery spaces, the design concentration of vapour in air shall be not less than 4.5 per cent and not more than 6.0 per cent at 20°C of the gross volume of the space to be protected including the skylight casing if fitted.
(29) Notwithstanding subsections (26) and (28), the volume of free air contained in air receivers located in any machinery space protected by smothering gas shall be added to the volume used for calculating the quantity of gas required.
The definition of "machinery space" from the Hull Construction Regulations includes any trunk to a machinery space, so it includes the funnel space, limited by 3.(26)(a) above.
http://laws-lois.justice.gc.ca/eng/regu ... .html#h-99
PART IX
FIRE PROTECTION FOR TANKERS AND COMBINATION CARRIERS
Interpretation
144. In this Part,
“machinery space”
“machinery space” means a machinery space of Category A and any other space containing boilers, oil fuel units, steam or internal combustion engines, generators, major electrical machinery, oil filling stations, refrigerating machinery, stabilizing machinery, ventilation machinery, air conditioning machinery or propelling machinery and any similar space and includes any trunk to a machinery space;