Cargo tank internal pressure head.

(a) For the calculation required under § 154.406(a)(1) and (b), the internal pressure head (h eq ), must be determined from the following formula: h eq = 10 P o + (h gd ) max where: h gd (the value of internal pressure, in meters of fresh water, resulting from the combined effects of gravity and dynamic accelerations of a full tank) = aβ Zβ Y; where: aβ = dimensionless acceleration relative to the acceleration of gravity resulting from gravitational and dynamic loads in the β direction (see figure 1); Zβ = largest liquid height (m) above the point where the pressure is to be determined in the β direction (see figure 2); Y = maximum specific weight of the cargo (t/m 3 ) at the design temperature. (b) The (h gd ) max is determined for the β direction, on the ellipse in Figure 1, which gives the maximum value for h gd . (c) When the longitudinal acceleration is considered in addition to the vertical transverse acceleration, an ellipsoid must be used in the calculations instead of the ellipse contained in Figure 1.