Personal Minimums: Deciding Before You Get to the Water
A newly certified diver is invited to make an 18 m/60 ft shore dive from an unfamiliar beach. The depth is within training, but the dive also involves surf, navigation, and an exit that may become harder as conditions change. Add unfamiliar equipment and an inexperienced buddy, and the certification card tells us relatively little about whether this particular dive is appropriate. Several ordinary demands have been combined before the diver has much independent experience handling them.
What aviation contributes
An instrument approach may permit a landing in weather that a qualified pilot sensibly declines to accept. Low cloud brings the transition from instruments to visual references closer to the ground; poor visibility may delay seeing the runway still further. Once it becomes visible, less time remains to assess alignment and stability, make corrections, or abandon the landing. A pilot with limited recent instrument experience can choose higher personal minimums for ceiling and visibility while retaining the option to approach published limits as proficiency develops.
FAA guidance recommends writing these limits down beforehand, avoiding reductions to accommodate today’s flight, and changing one variable at a time. Diving has comparable pressures: the charter is paid for, the gas is mixed, and the team has traveled.
Individual limits become team limits
For a recreational diver, a personal rule might require benign conditions and a knowledgeable buddy at an unfamiliar shore site. A technical diver returning after a layoff might reduce depth and decompression until relevant skills are again routine. Breathing a deco stage down to almost zero at 6 m/20 ft may be perfectly acceptable, provided adequate contingency gas remains available. Requiring exactly that much gas to satisfy the decompression obligation is demonstrably a bad idea for a rusty diver whose surface air consumption is higher than the rate used in the gas plan. In either case, the limit reflects present capability rather than the full scope of the certification.
Cave gas planning makes the team implications particularly clear. Consider two divers with equal starting supplies and consumption. If they penetrate to thirds and one loses the entire usable supply at the turn, the other diver’s remaining two-thirds must bring both out. Even assuming an exit identical to the entry, that consumes everything. There is no allowance for stress-induced increases in gas consumption, time to identify the failure and reorganize the team for gas sharing, or delays while confirming navigation and negotiating a silt-out at the failure site. Using the full third under those assumptions is a spectacularly poor plan.
Suppose Diver A proposes quarters instead. Diver B has an established personal minimum allowing no more than 20% of starting gas for penetration in a team of two. The team adopts that limit and turns with at least 80% remaining. That percentage is an illustrative personal limit, not a substitute for assessing the actual exit gas requirement.
“This rubs me the wrong way” expresses a concern that deserves attention. “I am uncomfortable extending penetration beyond 20% of gas use because that exceeds my established personal minimums” identifies a specific boundary and gives the team something concrete to plan around. Diver B does not have to prove that quarters are universally unacceptable to decline them.
Any diver can terminate any dive for any reason. The same discretion belongs in planning: each diver should be able to set limits based on experience, conditions, equipment, and team familiarity. Where those limits differ, the shared plan must satisfy the most restrictive applicable limit.
Establish them before the trip
Write rules that affect decisions, date them, and record why they change. Expand them following relevant training and demonstrated proficiency, with other demands initially held steady; tighten them when circumstances require it. Meeting every criterion still leaves anyone free to decline. Written minimums make the boundary clear before an appealing dive supplies reasons to negotiate it away.