Why is 18m set for OW?

[Blasto]

Yep.

The 60ft limit is there to keep novice divers from hurting themselves, at least in a dive op situation with rental gear. No one's stopping you from going as deep as you want with your own tanks. All in all, there's a lot less to go wrong at 0-60 ft than there is at 60-132. Being able to see the surface and be seen from it in typical good vis conditions helps too.

Everyone understands that, it's nothing new. The only question is why 60 and not 50 or 71. And there's a lot of reasons that converge on 60: nice round number, 1 minute ascent, roughly half the full limit.

 

[Bob DBF]

The 60ft limit is there to keep novice divers from hurting themselves...

Which is why the 60' recommended depth has been used for a long time. The OW training I had emphasized expanding your limits in a slow and controlled manner, since we did cert dives to 60', the new frontier started there. For divers trained at 30' their limit should start there, especially since I doubt they are trained on how to expand their limits from that point at all.

As @boulderjohn has been pointing out, a lot of information in scuba has been hanging on for so long no one has any idea where it came from, or why.


Bob

 

[DevonDiver]

This probably stems from PADI. On the PADI RDP, the maximum ascent rate is 60ft/18m per minute.

Thus, the 60ft/18m depth limit kept divers no more than 1 minute away from the surface.

A prudent distance/time that keeps the option of CESA ascent practicable for an error-prone demographic of novice divers.

Other agencies, not using the RDP ascent rate, opted for a round number - 20m/3ata.

 

[tursiops]

This probably stems from PADI. On the PADI RDP, the maximum ascent rate is 60ft/18m per minute.

Thus, the 60ft/18m depth limit kept divers no more than 1 minute away from the surface.

A prudent distance/time that keeps the option of CESA ascent practicable for an error-prone demographic of novice divers.

Other agencies, not using the RDP ascent rate, opted for a round number - 20m/3ata.

So, I should infer that folks trained by other agencies than PADI can hold their breath longer?

 

[Bob DBF]

This probably stems from PADI. On the PADI RDP, the maximum ascent rate is 60ft/18m per minute.

PADI was using the 60' depth for novices and 100' for divers advise, back prior to 1980 when the standard ascent rate was 60'/min. This was one of 16 pieces of advise in the manual of that time, which included surface with 300# of air, don't get too cold, maintain your equipment, take all the gear you need for the dive, stay with your buddy, equalize, and so on. Considering the space given it was a minor point, but was in the chapter review and probably on the final. If it was on the final my hat is off to @boulderjohn for calling it.

I was advised in '62 to restrict my depth until I got more experience, as problems get worse faster as you go deeper. Somewhere in between those dates the advice gained a number (60') and between '80 and the present it became more of a limit, rather than advise.


Bob

 

[boulderjohn]

The standard rate of 60 FPM was set in the 1950s by the US. Navy. PADI did not create the RDP until the 1980s, and it used 60 FPM becauses that had been the standard for about 30 years.

 

[TMHeimer]

Which is why the 60' recommended depth has been used for a long time. The OW training I had emphasized expanding your limits in a slow and controlled manner, since we did cert dives to 60', the new frontier started there. For divers trained at 30' their limit should start there, especially since I doubt they are trained on how to expand their limits from that point at all.

As @boulderjohn has been pointing out, a lot of information in scuba has been hanging on for so long no one has any idea where it came from, or why.


Bob

Agree that someone trained in up to 30' depth should start diving at that depth. Then through courses or mentors, expand deeper. Most of the time now it is similar to getting your driver's license on city streets then having the green light to go 70 on the interstate.