Maximum recommended safe descent rate for
scuba varies depending on the certifying agency but fall between 70 and 80 fpm.
Faster than that aggravates nitrogen narcosis. It can also cause joint pain and
HPNS.
Another danger escaping from a sub could be
shivering uncontrollably in cold water. It happened to me once when I was
diving with the FD and it’s something that doesn’t seem dangerous
but is when you literally lose all muscle control. A thick wet suit top would
probably be a good take along item in cold water.
Greg Cottrell
Project Manager
http://www.precisionplastics.com
P please consider
the environment before printing this email
From: owner-
Sent: Tuesday, August 24, 2010
12:40 PM
To:
Subject: Re: [PSUBS-MAILIST]
Escape from a K250 at 200 ft
Hugh Fulton created a "flooding" spreadsheet calculator back in early
May of this year. I just checked it and the results for a K-250 type sub
at 200 feet with one 2-inch flood valve comes out to total flood in 50
seconds. With one 1-inch valve that time is slowed to 200 seconds, and
with a 3/4 inch valve the time is 355 seconds.
I didn't have time to post the spreadsheet before the convention but will get
to it this week.
Jon
On 8/24/2010 4:06 AM, Alan James wrote:
Hi all,
I've put some facts & figures together re
flooding a K250 at 200 ft.
Firstly, sorry I move between metric & imperial.
I was brought up on
imperial then N.Z. moved to metric. The metric system
is great for these
soughts of calculations.
The first assumption is that the hull & hatch
area displaces 1,100 liters.
The hatch 100 liters & the hull 1000 liters.
The flow figures through a 2" pipe come from
table 2 on this link. It was the best I could find.
These figures are approximations as the flow rate
changes all the time. Also I'm not
taking into account how many or how fat the occupants
are.
To fill to half way with the 2" valve at 100 psi
the water will be coming in at 384 gallons per minute.
It will fill the 550 liters (132 gallons) in about 20
seconds. The air in the hull will be compressed
to half its size & will be an equivalent pressure
(14.7 psi) as at 33 ft.
To fill the hull from 1/2 to 2/3 the flow
pressure will be between 85 psi & 70 psi. About 340 gpm.
The volume to be filled is 183 liters ( 48 gallons
).This will take 8 &1/2 seconds. In terms of internal
pressure you have just gone from 14.7 to 29.2 psi
wich is the same as diving from 33 ft to 66 ft in
8&1/2 seconds.
To fill the hull to 3/4 the pressure will be from 70
to 55 psi about 300 gpm.
The volume to be filled is 92 liters ( 24
gallons ). This will take about 5 seconds. Again this is
equivalent to going down another 33 ft. to 99 ft.
Am being kicked off the computer for the night so
will leave it there.
But that is flooding so fast, I'd want to have my
hand on the valve as at that rate you'd blow
your ear drums for sure. It's best to equalize your
ears before they start feeling pain & in this
instance you can't reverse the pressure like
while diving, by ascending.
These figures are open for correction.
Regards Alan