Only if necessary! Asphyxiation warning mark for cargo transport units: The warning mark shall be rectangle. The minimum dimensions shall be 150 mm wide x 250 mm high. The word "WARNING" shall be in red or white and be at least 25 mm high. Where dimensions are not specified, all features shall be in approximate proportion to those shown. * Insert proper shipping name or name of tne asphyxiant gas used as the coolant/conditioner. The lettering shall be in captals, all be on one line and shall be at least 25 mm high. If the length of the poprt shipping name is too long fit in the space provided, the lettering may be reduced to the maximum size possible to fit. For example: CARBON DIOXIDE, SOLID. Additional information such as "AS COOLANT" or "AS CONDITIONER" may be added. The method of marking shall be such that this information will still be identifiable on cargo transport units surviving at least three months' immersion in the sea. In considering suitable marking methods, account shall be taken of the ease with the surface of the cargo transport unit can be marked.