49 states have adopted various versions of NFPA 58
nfpa 58 allows for filling to 42% of WC (containers up to 1200 gal, sg .504-.51)
Table 4-4.2.1 Maximum Permitted Filling Limit (percent of marked water capacity in pounds
Above ground over 1200 gal they allow 45% of water capacities and 46% for underground.
Table 4-4.2.2(a) Maximum Permitted Liquid Volume (percent of total water capacity): Aboveground Containers 0 to 1200 Gal (0 to 4.5 m3) allows for filling to 95% if the liquid is 130F (sg .504-.51, 80% @ 40F)
proper working OPD prevents that!