Here are the limits for the dives during this certification:
Wreck penetration limits.
The overhead environment poses three limits beyond the normal open
water constraints of depth, air supply and no-decompression limits:
1. Edge of light zone — You should never penetrate a wreck past
the point where you can see the natural light of the entrance.
For this reason, you do not make penetration dives at night or
in water so deep and murky that there is little or no natural
light visible from inside the wreck.
2. Linear distance of 40 metres/130 feet — The maximum total
distance you enter a wreck should not exceed 40 metres/130
feet from the surface, even if you’re still in the light zone.
3. One third of air supply — Wreck penetration uses the rule of
thirds for air planning. Use 1/3 of your air to penetrate (which
starts when you descend), 1/3 to exit and keep 1/3 in reserve.