202

THE COLLIERt GTIARDlAit

Januaky 23, 1914.

Siebe, Gorman and Co., London). The ordinary form)
for mining work, and a new form, designed for the
London Fire Brigade, were both tested. (2) “Weg”
(made at Altofts Colliery from the design by Mr. W. E.
Garforth). (3) “Draeger” (Draegerwerk, Lubeck).
The helmet and mouthpiece forms were both tested.
(4) “ Meco ” (Meco Manufacturing Company, Sheffield),
helmet and mouthpiece forms. (5) “ Aerophor ’
(Simonis and Co., Walthamstow). The experiments at
the Doncaster Coalowners’ laboratory were carried out
in co-operation with Mr. T. F. Winmill, chief chemist,
and Mr. J. Ivon Graham, chemist to Bentley Colliery.
Some of the experiments were made in the course of an
investigation which Dr. Haldane recently carried out,
with valuable help from Dr. M. S. Pembrey, lecturer
on physiology at Guy’s Hospital, for the London Fire
Brigade.

Many of the experiments were made with a view of
gaining general information rather than of bringing
out the merits or demerits of the different apparatus.
Defects or weaknesses, however, were noticed in each
form. Some of these defects seemed to be remediable
by taking special precautions in use, or by modifications
in construction. Other defects seemed to be of a more
radical kind.

A detailed account of the experiments, including a
description of the various apparatus, follows, from
which we extract certain portions.

In connection with the tests of the “ Proto ”
apparatus, experiments are described which illustrate
the dangers that may arise from a rescue apparatus
with an inadequate oxygen supply. It is pointed out
that when a man at rest breathes into and out of a. bag,
such as that of a rescue apparatus, and the oxygen
percentage is allowed to fall gradually, while the CO2
is absorbed, consciousness is sometimes lost without any
warning symptom. In most persons, however, there is
a distinct increase of breathing, and some subjective
uneasiness, before consciousness is lost. As a rule, the
first noticeable objective symptom is failure of the
limbs. After paralysis of the limbs the senses fail, one
by one, the sense of hearing being apparently the last
to disappear. Probably the power of thinking and
acting rationally is in reality affected first of all. The
subject always thinks, however, that he is all right, just
as does a man suffering from alcoholic intoxication.
In reality he may be acting in a blindly irrational
manner, and is very apt to be possessed with the fixed
idea of going on with what he is doing, regardless of
the threatening danger. If, with the bag of a rescue
apparatus containing a mixture of oxygen and nitrogen,
the oxygen supply of the bag were accidentally cut off,
as has often happened, it is evident that the wearer
would be in imminent danger. For the oxygen
percentage in the air breathed would rapidly fall,
until less than 10 per cent, of oxygen was present in
the bag, at which point dangerous symptoms would
develop rapidly. If the oxygen supply were simply
inadequate to meet the consumption, a similar, but
more gradual, running down of the oxygen percentage
would occur. In order to see what would happen if the
oxygen supply were far more than adequate to meet the
consumption during the rest, but inadequate to meet
the consumption during work, the following experiment
was made:—The subject (Mr. Phillips) was given the
“ Proto ” apparatus to wear. The bag was more or less
empty at the start, and contained only the air left in it
when it was taken up. The reducing valve had, without
the knowledge of the wearer, been set to give only
1 litre per minute, instead of the usual 2 litres. The
oxygen was turned on, and Mr. Phillips was asked to
walk at an ordinary pace. After he had gone about
150 yards his face began to turn of a dull colour, but he
did not notice anything wrong. A short distance
further his face was alarmingly blue, but he still said he
felt all right. Just afterwards he began to stumble
and we caught him and removed the mouthpiece. A
few seconds later his colour again became a healthy
pink, and at the same time everything seemed to him to
brighten up, and sounds to become much louder. Had
he been allowed to go a few yards further he would
certainly have fallen over unconscious, and if he had
been underground in a dangerous atmosphere the
mouthpiece might have been knocked out of his mouth,
with fatal results.

The experiments show clearly that it is risky to cut
down the oxygen supply, during even moderate exertion,
to as little as 1 litre, unless the bag contains little or no
nitrogen, which is seldom the case until after the
apparatus has been runningfor some time. It isthecustom
in one district to limit the oxygen supply to as little as
0 75 litre. This seems an invitation to serious accidents;
in any case, it limits exertion to something quite trifling
unless the by-pass is constantly used. If, however, the
nitrogen in the bag and lungs is practically got rid of

before starting, no harm will result, as the emptiness of
the bag will give timely warning to stop or fill up the
bag through the by-pass.

For walking on the level at 32 miles per hour
and carrying the apparatus, 2 litres of oxygen per
minute appeared to be sufficient for all persons; but
with increase of speed more oxygen was required. It
seemed distinctly easier to walk with the apparatus,
breathing almost pure oxygen, than, without it,
breathing ordinary air. In order to permit of really
hard work, such as a fireman might probably be called
upon to do, the oxygen supply in the fire brigade
apparatus was increased to 3 litres per minute. In a
mine an exertion greater than corresponds to an average
oxygen consumption of 2 litres per minute will be
seldom needed; but it should be clearly understood that
with extra exertion—as, for instance, in ascending an
incline—more than 2 litres may be quite easily con-
sumed, in which case the by-pass should be used to
replenish the bag.

Experiments with the “Weg” apparatus are next
described. The present defects in the “ Weg ” apparatus
appear to be—(1) resistance to breathing; (2) liability
to waste of the oxygen through the blow-off valve and
half-mask ; and (3) liability, unless great care is taken,
to leakage inward, presumably at the half-mask. It
seems probable that all these defects could be remedied,
in which case the apparatus would be an extremely
perfect one. In its present form great care and
experience are needed to avoid waste of oxygen on the
one hand, and serious leakage inward on the other. The
resistance to breathing is also so great as to limit unduly
the power of doing hard work.

Leaky Helmets.

The committee have made a number of experiments
with the “Draeger” apparatus, and particularly with the
helmet form. Many of the experiments were made, not
on quite new apparatus, but on those found in actual
use. Certain importants defects were found.

On putting on helmets and carefully blocking the
inspiratory and expiratory openings, with the pneumatic
cushion blown up tight, Dr. Haldane found that he could
still inspire and expire, though slowly, through leakage
past the pneumatic cushion. The cushion itself bulged
in an irregular manner when blown up, leaving chinks
through which air easily penetrated. This was owing
to the rubber having gradually become stretched. There
were also leaks in both cushions, so that the cushions
gradually become slack unless frequently pumped up.

With a perfect pneumatic cushion the leakage was
less, but in every helmet tested it was present, and it
was easy to fill the lungs completely in a few seconds by
an inspiratory effort. In this test there is, however,
considerable pressure in an inwards direction, and it
may be argued that such pressure never exists during
actual use of the helmet, so that the actual leakage may
be so small as to be unimportant. The helmets have
also been tested hundreds of times in smoke chambers
without any harm resulting to the wearers. It is
necessary to point out in the very clearest manner that
such reasoning is fallacious. It is probable that as a
general rule the atmosphere in smoke chambers used
for practice is not poisonous at all. In the second
place, the smoke or fumes do enter the helmet to some
extent, and can easily be smelt; and in the third place,
there is, during any serious exertion, such as what would
be required in an attempt to rescue an unconscious man,
very considerable alternating positive and negative
pressure in the helmet. On connecting a manometer
with the interior of the helmet and walking at about
4 miles an hour for two or three minutes, alternating
positive and negative pressures of 6 in. of water were
observed.

Helmets were tested in air containing coal gas, and
after these observations Dr. Haldane says he could come
to no other conclusion than that the helmet of the
“ Draeger ” apparatus (and the same applies to the
“Meco” helmet) is unsafe, even when the pneumatic
tube is in perfect order and very tightly pumped up.
The probability is that in actual practice the pneumatic
tube will be more or less old and stretched, and that the
pneumatic tube will not be very tightly pumped up, in
which case the helmet will be very unsafe. With the
mouthpiece attachment the whole apparatus can be
tested for tightness by suction at the mouthpiece.
The blow-off valve makes a test with positive pressure
very difficult. No leakage could be found in the appa-
ratus tested.

Size of Purifiers.

Further experiments with “Draeger” apparatus
showed that the size of the present purifier is inadequate.
It broke down long before the oxygen supply was
exhausted. A man relying on the gauge readings as a
measure of the time during which the apparatus would
last might be disabled in a dangerous atmospheie.

This serious defect would be remedied by supplying a
considerably larger purifier. The existing purifier,
doubtless, lasts sufficiently for two hours of the com-
paratively light work of an ordinary “ practice ” in a
smoke chamber, but might easily prove unsafe in actual
work underground. As the “Draeger” purifier con-
tains a comparatively small amount of alkali, it heats
up very rapidly and becomes extremely hot. The heat
seems to be favourable to absorption of C02, though it
doubtless causes a good deal of moisture to be given off.
The metal and rubber pipes leading onward from the
purifier seem to be quite efficient in cooling the air to
about the surrounding temperature. The hot cartridge
did not burn the back in any of the experiments.

In another experiment on the composition of the air
in the helmet, the air circulation through the purifier
was found to be 34 litres per minute, with an oxygen
delivery of 2 litres. This is considerably less than
the injector is supposed to deliver (about 60 litres),
though very little less than what was actually delivered
(41’6 litres) in perfectly new apparatus after 75 minutes
of use. When the mouthpiece is used instead of the
helmet, the trouble from CO2 with the “ Draeger ”
apparatus is greatly diminished, since the large dead
space in the helmet is got rid of, and the wearer gets
the full benefit of whatever air is delivered from the
purifier.

No further investigation was made of the causes of
the failure of the injector to deliver the quantity of air
which is stated to be delivered when the apparatus is
quite new, or whether it is a common thing for the
delivery to fall off while the apparatus is in use, as was
the case in the only experiment in which this point was
tested. It seems probable enough that such falling-off
is due to increasing resistance in the purifier, but this
does not explain the fact that even with a fresh purifier
the air circulation is apt to be much below the stated
quantity.

Most of the criticisms applicable to the “Draeger”
apparatus apply equally to the “Meco.” The Committee
found the helmet to be just about as leaky as the
“ Draeger ” helmet, and the large air space in the front
of the helmet seemed about equally disadvantageous
from accumulation of CO2 in it.

With regard to the “ Aeroph or ” apparatus, the
committee say: “ It seems quite clear from these
experiments that the 4 Aerophor/ in the forms which
we have tried, is still in an experimental stage, and that
the experiments required ought not to be made in a
dangerous atmosphere underground until the main
defects of the apparatus have been successfully elimi-
nated. With a proper purifier, and an airtight apparatus,
there seems to be no reason against the successful
application of liquid air for rescue purposes. Liquid
air has the advantage that it furnishes a very cool air
supply to the wearer; but the practical difficulties in
using it are very serious, and large quantities of it must
necessarily be wasted on account of the difficulty in
handling it, or obtaining any practical measure the rate
at which it is evaporating when once it is outside a
vacuum flask.”

General Conclusions.

Dr. Haldane’s concluding remarks are given in full:—

I shall now endeavour to summarise the results of
the tests, and at the same time refer to a few points not
hitherto discussed. In some respects the tests applied
in the course of our investigations have been more
stringent than in former investigations. The reason for
this is that experience has shown that every weak point
in an apparatus is sure to appear during actual use
underground, and with consequences which may be
fatal. Special care and intelligence will always be
required in the use of mine rescue apparatus, but cannot
be relied on beyond a certain point. Several of the
recent fatal accidents in this country have occurred to
men who were specially skilled and careful. It has also
been kept in mind that an apparatus, to be of any use,
must permit of a reasonable amount of continuous
exertion. The apparatus must suit itself to the man
and his work, not the man and his work to the apparatus.
In comparing different forms of apparatus, allowance
must be made for the fact that they are all capable of
modification and improvement, so that defects which
have appeared in the tests may be removed in later
forms of the same type of apparatus. In the actual
tests something has also depended on whether or not
the individual apparatus used was in perfect working
order. The experiments were confined to forms of
apparatus in actual use in this country. For this reason
alone no experiments were made with the “ Tissot ” or
“ Pneumatogen ” apparatus.

Convenience during Actual Use and in Preparation for
Use.—Several points are very important in connection
with the actual uses of a rescue apparatus in mines.
The first is that both vision and hearing ought to be as