指的工厂防火，这句话，the level和grade是什么意思

chgdong213

Within a fire-scenario envelope, when the collapse
of unprotected structures that support equipment could result
in substantial damage to nearby fire-potential equipment, fireproofing
should be considered for the vertical and horizontal
steel members from grade level up to and including the level
that is nearest to a 30-ft (9.1-m) elevation above grade (see
Figure 6).

chgdong213

这句话确实不好理解，尤其是grade level