# 154.407 Cargo tank internal pressure head.
(a) For the calculation required under § 154.406(a)(1) and (b), the internal pressure head (h<sub>eq</sub>), must be determined from the following formula:
h<sub>eq</sub> = 10 P<sub>o</sub> + (h<sub>gd</sub>)<sub>max</sub>
where:
h<sub>gd</sub> (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
<sup>3</sup>) at the design temperature.
(b) The (h<sub>gd</sub>) <sub>max</sub> is determined for the β direction, on the ellipse in Figure 1, which gives the maximum value for h<sub>gd</sub>.
(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.