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SHORT COMMUNICATION
Submarine Escape from Depths of 30 and 60 Feet:
41,183 Training Ascents Without Serious Injury
S¸enol Yildiz, Hakan Ay, Alp Gu¨nay, Serdar Yaygili,
and S¸amil Aktas¸
YILDIZ S, AYH, GU
¨NAY A, YAYGILI S, AKTAS¸ S¸. Submarine escape
from depths of 30 and 60 feet: 41,183 training ascents without serious
injury. Aviat Space Environ Med 2004; 75:269–71.
Introduction: In the case of a submerged, disabled submarine, survi-
vors may be forced to escape by entering the water and ascending
rapidly to the surface. The large pressure changes involved may produce
pulmonary barotrauma, arterial gas embolism, or barotrauma. To assess
the likelihood of such injuries, we retrospectively evaluated medical
problems due to submarine escape training among military personnel.
Methods: We evaluated 41,183 controlled ascents performed over the
past 21 yr in the escape training tank at Go¨ lcu¨k-Kocaeli, Turkey. Each
trainee performed two free ascents from 30 ft and two hooded ascents
from 60 ft. Before participating, candidates were screened by physical
examination, spirometry, and chest X-rays; ear examinations for baro-
trauma were made after ascents. If a trainee failed to exhale properly
during ascent, an instructor aborted the ascent and took him to a bell or
side recess of the tank. Results: No record of pulmonary barotrauma or
other major complications were found. Middle-ear barotrauma was
observed following 1,643 of the ascents (4.1%), with rupture of the
tympanic membrane in 35 cases. Discussion: Submarine escape ascents
can be safely performed provided that subjects are medically screened
and well trained.
Keywords: air embolism, submarine escape, pulmonary overinflation.
MODERN SUBMARINES that meet the highest
possible safety standards are rarely disabled, but
it is still necessary to plan for contingencies. If an acci-
dent produces a submerged, disabled submarine, there
are two methods of saving survivors’ lives. The pre-
ferred and safer method is “rescue,” which means evac-
uating the survivors into another submersible vessel. If
that is not possible, survivors must exit the submarine
through a hatch into the sea and make a buoyant ascent
to the surface (3). Survivors who escape from a subma-
rine are likely to be suffering from various combina-
tions of traumatic injuries and burns from the original
accident, to which the ascent may add barotrauma,
arterial gas embolism, decompression sickness, hypo-
thermia, and near-drowning (9).
In a free ascent, the submariner has no equipment
over his head and must continuously exhale the ex-
panding air from his lungs all the way to the surface to
prevent potentially fatal consequences. In a hooded
ascent, a head enclosure allows him to inhale and ex-
hale and, therefore, requires less self-discipline. Al-
though complex systems to support respiration during
escape were used by various navies in the past, simpler
hoods are now used (6).
Some navies train submariners in escape techniques
using a deep tank called a submarine escape training
tank (SETT). Such training allows the personnel to un-
derstand the submarine environment and experience
the stresses of ascent under the safest possible condi-
tions, and can also serve as a screening test for candi-
date submariners. The efficacy of training is shown by a
report from the Royal Navy that states during the pe-
riod 1954–1993, the incidence of pulmonary barotrau-
mas (PBT) among requalifiers was less than half that for
initial trainees (1).
Despite its advantages, some navies are reluctant to
perform SETT training because of its high cost and the
fact that such training doesn’t reflect realistic open-sea
conditions (4). In addition, trainees may suffer some of
the same decompression effects associated with real
escape. For instance, it has been reported that subma-
rine escape training is associated with an incidence of
PBT of 0.1 to 0.6 per 1,000 escapes for hooded ascent
and 1 to 19 per 1,000 for free ascent (8). We believed that
a new, up-to-date evaluation was needed to allow a
better evaluation of the risks and benefits of SETT train-
ing. In this study, the data were derived from the
records of submarine escape training in the Turkish
Navy between 1981 and 2001.
METHODS
Candidates have to complete escape training to qual-
ify as submariners, and then repeat it every 2 yr until
age 35. All candidates fill out a health status question-
naire and undergo a detailed physical examination by a
From the Gu¨ lhane Military Medical Academy, Haydarpas¸a Train-
ing Hospital, Department of Underwater and Hyperbaric Medicine,
Istanbul, Turkey (S¸. Yildiz, H. Ay), the Go¨lcu¨k Naval Hospital, De-
partment of Gastroenterology, Go¨lcu¨ k/Kocaeli, Turkey (A. Gu¨ nay),
the Submarine Training Commend, Free Escape Tank, Go¨lcu¨ k/Ko-
caeli, Turkey (S. Yaygili), and Istanbul University, Istanbul Faculty of
Medicine, Department of Underwater and Hyperbaric Medicine,
C¸ apa/I
˙stanbul, Turkey (S¸. Aktas¸).
This manuscript was received for review in May 2003. It was
revised in June, September, and October 2003. It was accepted for
publication in November 2003.
Address reprint requests to: Senol Yildiz, Gu¨ lhane Military Medical
Academy, Haydarpas¸a Training Hospital, Department of Underwater
and Hyperbaric Medicine, 81100 Kadıko¨y/I
˙stanbul, Turkey;
syildiz@gata.edu.tr.
Reprint & Copyright © by Aerospace Medical Association, Alexan-
dria, VA.
269Aviation, Space, and Environmental Medicine •Vol. 75, No. 3 •March 2004
diving medical officer. A chest X-ray is used to rule out
active tuberculosis, lung cysts, or bullae, and a sinus
X-ray is obtained if indicated. Spirometry was added in
1994. Subjects are excluded from training for abnormal-
ities in their physical examination, X-rays, or spirome-
try (i.e., if forced vital capacity (FVC), forced expiratory
volume in one second (FEV1) or FEV1/FVC are less
than 80% of predicted values). Middle ear examinations
are conducted after ascent and squeezes are recorded if
there is evidence of barotrauma or tympanic membrane
rupture; under this procedure, a squeeze cannot be
specifically assigned to ascent or descent. Candidates
who are unable to perform escape training for some
reason or had transient health problems are permitted
to complete the training later.
The Turkish Navy performs escape training in a SETT
located in Go¨lcu¨k-Kocaeli. The tank is 60 ft tall and 18 ft
in diameter. Compartments on the side walls at depths
of 30 ft and 60 ft allow simulated exit from a disabled
submarine into deep water, followed by ascent to the
surface. Emergency recesses in the sidewalls at 50 ft and
10 ft can be used by instructors to divert a trainee who
is having difficulty during ascent, and an open bell is
positioned to provide an additional stopping place at a
depth appropriate for the specific profile. There is a
recompression chamber at the upper deck that is al-
ways ready for immediate use during training.
The free ascents are performed from 30 ft at a rate of
375 ft min
⫺1
using the Steinke apparatus (Switlik
Parachute Co. Inc, Trenton, NJ) without its hood. There
are two types of hooded ascents included in the data-
base: 1) Most were performed at an ascent rate of 425 ft
min
⫺1
using the Steinke hood starting from the com-
partment at 57 ft, which was designed in 1981 to sim-
ulate submarines in use at that time. This involved
complex manual procedures and slow compression of
the escape trunk with resultant exposure to high partial
pressures of nitrogen and carbon dioxide; the escape
trunk was partly flooded and once the trainee exited
into the tank, the instructor physically controlled the
ascent rate, especially during the last 30 ft. 2) In 1999,
the Turkish Navy began using Mk 10 SEIE hoods (Bea-
fourt Airsea Equipment Limited, Birkenhead, UK). At
the same time, a new compartment was added to the
chamber at 55 ft to simulate escape from the newer class
of submarines and to simplify procedures. A small pro-
portion of the hooded ascents were performed using an
ascent rate of 590 ft min
⫺1
with the SEIE hood, starting
from the 55-ft compartment, which was fully flooded
before escape.
Before their initial exposure to the tank, trainees are
given a detailed theoretical education by experienced
instructors. The training protocol includes two free as-
cents and two hooded ascents. For each ascent, the
trainee enters the appropriate training compartment by
walking through an entrance hatch. The compartment
is closed and its pressure is then increased at a rate
equivalent to descent at 75 ft min
⫺1
. In case of ear
symptoms, it is common practice to stop, ascend a few
feet to clear the ears, and then continue compression.
When pressure in the compartment matches water
pressure at that depth in the tank, the compartment is
flooded, the hatch is opened and the trainee moves into
the tank to perform the ascent. An instructor closely
observes the trainee during ascent, and those who do
not exhale properly are stopped and taken to the bell or
a side recess for removal from the tank and examination
by the doctor.
RESULTS
We reviewed the records from a total of 12,160 appli-
cations for initial or periodic training during the period
from 1981 through 2001. Of those, 1,055 (8.6%) were
screened out due to respiratory tract infection (30%),
abnormal spirometry (25%), wax in the external ear
canal (25%), subjective complaints (feeling bad or not
ready to escape) (10%), and other medical conditions or
current use of medication (oral steroids, muscle relax-
ants, digoxin, psychotropic drugs, etc) (10%).
The remaining 11,105 applicants performed a total of
41,183 training ascents. The initial 30-ft free ascent pro-
duced middle-ear barotraumas (MBT) in 741 cases
(6.7%), and those trainees were excused from the sec-
ond free ascent. The 10,364 second free ascents pro-
duced MBT in a further 152 cases (1.5%). A trainee who
experienced MBT at any stage in the training sequence
was stopped, but was allowed to complete training a
month or more later.
A total of 10,212 trainees made a first escape from 60
ft, 98.5% with the Steinke hood and the remainder with
the SEIE hood. Some 9,462 trainees completed the sec-
ond 60-ft ascent, thus completing the entire training
sequence. There was no significant difference in the
outcomes for the two hoods. MBT occurred in 710
(7.0%) of the first ascents and 40 (0.4%) of the 9,502
second ascents. Thus, the rate of MBT was 4% for all
ascents. Of the affected individuals, 35 (2.1%) mani-
fested tympanic membrane ruptures. There were no
cases of PBT, arterial gas embolism, decompression
sickness, drowning or near-drowning, or traumatic in-
jury.
DISCUSSION
A number of studies have reported the occurrence of
pulmonary problems (PBT) and arterial gas embolism
during submarine escape training. The highest inci-
dence (3.6%) was reported by Ingvar at al. in a prospec-
tive study based on symptoms, signs, and chest X-ray
findings (5). On the other hand, Ikeda at al. reported no
PBT or embolism in their study of Japanese Navy as-
cents from 10 m using the Steinke hood (4). They sug-
gested that the this safe record might reflect the rela-
tively shallow depth, the use of a tank-entry hatch on
the bottom rather than the side wall of the compart-
ment, the presence of an open bell near that hatch, the
availability of two emergency recesses, and very careful
medical screening of the trainees.
Routine spirometry has been carried out during the
medical examination of military and commercial divers
for many years. An association between the low values
of FVC and PBT in submarine escape tanks was inter-
preted as a statistical association but was not used as an
index of risk (7). Brooks et al. observed that among
SUB ESCAPE WITHOUT FATALITY—YILDIZ ET AL.
270 Aviation, Space, and Environmental Medicine •Vol. 75, No. 3 •March 2004
several measurements that indicated pulmonary ob-
struction, a low value for FVC was the variable associ-
ated with the occurrence of PBT during ascent (2). They
concluded that screening out persons with an abnor-
mally low FVC might prevent up to 25% of PBT inci-
dents in submarine escapes and perhaps in diving ac-
cidents (2). Since 1994 we have disqualified applicants
with FEV1, FVC, and FEV1/FVC of less than 80% of
predicted values, and we assume that this procedure
has contributed to the absence of PBT in this study.
Tetzlaff et al. recommend the assessment of expiratory
flow rates in addition to conventional spirometry for
screening diving candidates (7), and we plan to add
peak expiratory flows of 25–50 and 75 as a test for
future trainees.
The occurrence of false-negative findings in plain
film radiography makes it desirable to adopt comput-
erized tomography (CT) for the radiographic assess-
ment of PBT to evaluate the lesions and to characterize
the accident, since even minor forms of PBT are consid-
ered to contraindicate future diving (7). However, the
high cost of CT and absence of PBT in our experience
mean that we cannot use chest CT as a screening test for
our trainees. Our MBT rate (4%) may be lowered by a
slower compression during the training. We conclude
that submarine escape ascents can be safely conducted
provided that the subjects are medically screened and
well trained.
ACKNOWLEDGMENTS
We are all thankful to Dr. Tauland Qyrdedi and Akın Toklu for
their collaboration.
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271Aviation, Space, and Environmental Medicine •Vol. 75, No. 3 •March 2004
