  In a recent $\Z_{12-I}$ orbifold model, an approximate $Z_2$ symmetry which
forbids the baryon number violating operators up to sufficiently high orders is
found. The dimension-4 $\Delta B\ne 0$ operators of the MSSM fields occur at
dimension 10. The effective dimension-5 $\Delta B\ne 0$ operators derived from
these are harmless if some VEVs of neutral singlets are O(1/10) times the
string scale. The main reason for forbidding these $\Delta B\ne 0$ operators up
to such a high order is the large order N=12 of $\Z_N$ since the $H$-momentum
rule is $(-1,1,1)$ mod (12, 3, 12). For a lower order $N<12$, the $\Delta B\ne
0$ operators would appear at lower dimensions.
