Some hazards, even high-level ones, don’t make sense with a high Hardness value. In those cases, you can skip the Hardness and use the HP values from table 2–7: Hit Points on page 63. Especially for complex hazards, you might want to divide the durability over multiple sections, located in different positions, to encourage teamwork and mobility.
This reference is outdated. The table mentioned used to be on page 63 of the Gamemastery Guide, and it used to be titled "Table 2-7: Hit Points." Now it resides on page 118 of GM core, and it is simply titled "Hit Points." This needs to be flagged for errata.