Risk Management Question: Flying after Shallow Dive

[Scraps]

Serious question:

Relative in town for brief vacation wants to do a shallow drift dive on spring-fed river.

Schedule is getting squeezed, and the only opportunity may be the morning of her departure.

Deepest spot on this stretch of river is about 21 feet. Average depth would be 12-15 feet for about 45-50 minutes. We'd be out of the water by 10:00 a.m. Her flight is at 7:00 p.m.

My inclination is to adhere to the 18-hour rule, even though the opportunity for nitrogen loading seems negligible, because I'm not comfortable with deliberately planning to deviate from published standards.

Is this the correct response, or would that be too persnickety?

 

[tursiops]

Using USN Table 9-7, a 25 FSW air dive for 1 hour puts you in Pressure Group D.
Table 9-6 says to wait 1h45min before ascending to altitude in a pressurized aircraft (8000 ft equiv).
At 20 FSW, it is PG C, with no time required before flying.
20 FSW is roughly 21 FFW.
It would seem your 9h wait before flying is ample.
If you want a bigger cushion, use Nitrox.

 

[inquis]

FWIW, the 18 hr timeframe is the recommendation for repetitive diving. The single dive, blanket recommendation is 12 hrs.

 

[tursiops]

FWIW, the 18 hr timeframe is the recommendation for repetitive diving. The single dive, blanket recommendation is 12 hrs.

It might be interesting for folks to see the report on how the 12 and 18h recommendations were arrived at. Dives tested were at least 40 ft deep.
The full workshop report is attached.
An interesting report summarizing the history and conclusions is also attached.