| Show self contained rescue apparatus by W R ELLIOTT under recent state legislation the provision of portable rescue apparatus has been made legally obligatory at coal and mines in several states no definite steps have been taken as yet however to ensure that the apparatus provided shall be as safe as practicable and the heavy responsibility of deciding what apparatus to select how far to trust to it in dangerous atmospheres and what form of training to arrange for has devolved on the owners and managers of mines the serious nature of this responsibility has hardly been fully realized as yet but the fact that a number of valuable lives have been lost through the use of the apparatus has shown how important is the question of safety if the apparatus was only applicable directly for rescue purposes there would seem to be still considerable doubt whether practical experience is likely to justify its use but it has often proved of service in dealing with actual or suspected fires and thus indirectly averting danger and it has occasionally been useful under other circumstances the aim of a self contained rescue or breathing app apparatus aratus is to supply the wearer with a constantly atmosphere which is quite independent of the surrounding atmosphere A atmosphere mo sphere need not have the same composition as ordinary air all that is necessary is that it should contain sufficient oxygen to support life and ordinary activity and that no other gas of a noxious character should be present in noxious proportions pure atmospheric air has the following composition by volume oxygen 2091 2094 nitrogen carbon dioxide prom from the point of view of respiration the nitrogen is a physiologically indifferent gas playing the part of a mere it might be replaced by another indifferent gas such as hydrogen or methane or by oxygen pure oxygen can be breathed for many hours though not indefinitely without any ill effect and during hard muscular work seems to be of distinct advantage on the other hand any marked fall in the oxygen percentage is disadvantageous and when the oxygen falls below 10 per cent consciousness may be partly or wholly lost and life endangered carbon dioxide is by no means a physiologically indifferent gas its effects will be described below in a self contained rescue apparatus the authority for the statements made in this article is found in the reports of various safety and investigating committees wearer always breathes into and out of a bag arrangements being made for replacing the oxygen removed from the air of at the bag by respiration and absorbing or otherwise removing the carbon dioxide given off in the expired air several types of apparatus are in use in the first and most usual type the oxygen in the air of the bag is constantly replenished by pure oxygen from a steel cylinder while the carbon dioxide is removed by caustic alkali such as soda or potash in a second type the oxygen is renewed by a stream of air or oxygen from a reservoir in which liquid air or liquid oxygen is evaporating in a third type the expired air is passed through a substance such as oxy lith which has the property of absorbing the carbon dioxide and moisture and at the same time liberating sufficient oxygen to replace what has been absorbed in respiration requirements of rescue apparatus before passing to a description of experiments peri ments made with different forms of apparatus it is necessary to discuss in some detail the physiological requirements of a rescue apparatus it seems self evident in oxygen coa CO given air breath fumed off per ed per av vol no of per min min in min in of each breaths in litres laitres li tres litres laitres litres laitres breath per min rest in bed 77 1 rest standing 1 walking at 2 miles per hour walking at 3 miles per hour 1065 walking at 4 miles per hour 1595 1395 1 walking at 4 miles per hour 2005 1788 walking at 5 miles per hour 2543 2386 1 the first place that if such an apparatus is to be of any real use it must be so designed as to permit the wearer to do a reasonable amount of work with safety and for a sufficient time an apparatus would be of little use and would be a source of much risk and anxiety if it were liable to break down under such ordinary exertions as walking along a level mine road or ascending an incline or helping to rescue an unconscious man the apparatus ought also to be capable of working efficiently for some definite time A period of two hours would seem to be reasonable and is now generally recognized as a minimum for apparatus to be used in mines in any case there ought to be some means by which the wearer can know definitely how much time he can count on if the apparatus were to break down unexpectedly in an atmosphere the result would quite probably be death for cutting off the oxygen supply or hindering the discharge of carbon dioxide CO by the lungs would cause loss of con ness very rapidly especially durin muscular exertion and thus would be ea dangerous in an at ai mo sphere even if help were near laabi ity to failure of some essential part of rescue apparatus would in fact be nearl as dangerous as similar liability to failer in an aeroplane the amounts of oxygen absorbed in re pi ration of carbon dioxide given off an of air breathed vary greatly with a exertion it should be noted also that tl th amount varies according to the amount i muscle used in the exertion thus even e haisting hau sting work with one arni arm as for i stance in sawing wood will not much h mor moi than double the absorption of oxygen whereas work with both legs as in walkin fast or ascending an incline may inarea it ten times the following table fr fro average actual measurements in the cas ca of a man of about average height ail ai weight will give some idea of the inarea in respiratory exchange and in the volun volum of air breathed during the exertion 0 v walking on a level field without load in heavier work such as ascending an incline or running the oxygen consumed may amount to three litres laitres a minute while the volume of air breathed runs up to over litres laitres a minute the oxygen and CO are measured at and mm nearly 30 inches barolet ric pressure at ordinary room temperature the volumes would be about 6 per cent greater had the subject of experiments been carrying a rescue apparatus the 99 ures would have probably been about 2 1 per cent higher since a rescue apparatus weighs about 25 per cent of the weight of the man the figures will also vary some j what for different individuals in the average case the consumption of oxygen slightly slight exceeds two litres laitres per minute while wearing an apparatus and walking at about fours four miles per hour from these data it is clear that in order orda to enable a man wearing an apparatus to walk along a level mine road at an orui j nary speed of about three and one half hair miles per hour an oxygen supply of about two litres laitres per minute is needed in order to prevent risk of the oxygen in the bag run ning down this is the supply ordinarily arranged for by the makers of the alpar atus provided with a constant oxygen supply from a s teel steel cylinder for severe work a supply of three litres laitres per minute would be needed restricting the supply during work means restricting the work and incurring the grea great t risks referred to below incident to deficiency of oxygen A supply of two litres laitres per minute ought to be regarded as a minimum when a man is walking about or performing other moderately hard work the store of oxygen carried ought also to be sufficient to maintain this supply for two hours or whatever other period the apparatus is meant to be used for design of purifier it seems equally clear that the purifier for carbon dioxide ought to be so designed as to last for at least the same period as the oxygen supply it is the more necessary to be certain of this since when at least the oxygen is derived from a steel cylinder the consumption of the oxygen can be read off on a gauge while there is no means of gauging the rate at which the purifier is being used up for this reason it has been adopted as a standard requirement that with a two hour apparatus the purifier should last for at least two hours with a person walking at a rate of three and one half to four miles per hour the complete failure of a purifier implies imminent danger as will be pointed out below and it is quite unjustifiable to run any risk in this direction it may also be well to point out in the clearest manner that a purifier which lasts perfectly well during a two hour practice in a smoke chamber with but little serious muscular work may break down hopelessly in a mine where a man may be continuously walking about and doing other considerable work supply of air the next point to consider is the supply of air for breathing it will be seen from froin the table that about fifty litres laitres of pure air per minute would suffice for such work as walking at four miles per hour wearing a rescue apparatus A minimum requirement is therefore that the pipes calves etc should be such that this amount of air can be comfortably obtained any undue resistance to the breathing would cause great distress and might be a source of danger the matter is not so simple however as as might at first sight appear for causes may represent be present which greatly increase the quantity of air required for a given amount of work the chief of these causes is the I 1 presence of CO in the inspired air if the purifying arrangement is acting imperfect ly or if a helmet or mask is worn and the design besign is such that part of the expired air ea is 3 re inspired owing to the existence of a o called dead space the inspired air will contain a certain proportion of coy CO to render the effects of this intelligible it is necessary to consider how the breathing is normally regulated besides the air taken in or expelled at each breath the lungs contain at any moment a large additional quantity of air much of which can be expelled by a deep expiration in the air cells or alveoli to which the bronchial tubes lead the composition of this air can easily be ascertained by catching and analyzing some of the last part of the expired air it was found by mr priestly and mr haldane that the percentage of CO coz in this air is very remarkably constant provided that the barometric pressure does not alter much the breathing is in fact so regulated regulate as to maintain a constant percentage of CO 56 per cent on an average in the alveolar air if the production of CO coz in the body increases as during muscular work the breathing at once increases sufficiently to keep the alveolar CO coz percentage almost constant if coa CO is present in the inspired air a similar effect is produced thus if 28 per cent of coa CO were present in the inspired air the breathing would be nearly doubled since it would take twice as much of the inspired air to keep the alveolar coa percentage at about 56 per cent if by voluntary forced breathing the alveolar CO cog percentage is lowered all desire to breath ceases for a time a condition of so called apnoea ap noea being produced so efad is the regulation that a deficiency of 02 per cent in the alveolar CO coa produces apnoea whereas an excess of 02 per cent doubles the breathing even with the breathing increased by muscular work to litres laitres as in the sixth series in the table the alveolar CO percentage had only risen to 62 per cent had there been 3 per cent of CO COs in the inspired air in this experiment the breathing would have increased to nearly double what it was i 1 e to about ninety litres laitres wilh such a demand upon it however breathing would be near the end of its capabilities distress would be very great and the resistance of pipes valves etc in an ordinary rescue apparatus would be very serious with any further increase in the rate of muscular work or in the percentage of CO in the inspired air the breathing could no longer deal with the conditions and the alveolar coa percentage would become so high as to produce toxic effects with partial or complete loss of consciousness how breathing Is increased the experiments described below will show how easily this result may occur or the breathing may at any rate be so much increased by CO as to make anything but slight exertion impossible A person at rest can quite easily compensate by deeper breathing the presence of 3 per cent or 4 per cent of coa CO in the inspired air and the subjective effect of 3 per cent is so slight as not to be noticeable but to double the breathing after it has already been increased to perhaps six or eight times its normal amount during rest is a very different matter it has sometimes been supposed that the effects of CO are neutralized by an increased oxygen percentage this is not the case A given percentage of CO produces about the same effect on the breathing whether or not the oxygen percentage has been largely increased apart from excess of CO coz in the inspired air the breathing may be much increased by rise of body temperature and this is an important matter in mines where men of often ten have to work in very warm and moist air the breathing is increased in two ways in the first place the discharge of CO cco from the body is much increased by a rise of body temperature and secondly the percentage of CO coa in the alveolar air is regulated at a lower level so that for a given discharge of CO coa more air is breathed the effect of rise of body temperature pera ture on the breathing during muscular exertion is very distressing As an example of this may be quoted the experiences of professor A E boycott in a very warm cornish mine he had been engaged for some time in collecting samples on the bottom levels of the mine when he began to feel affected by the heat and found that his temperature was in order to get to the shaft bottom it was necessary to climb several ladders each of about three fathoms in length in a letter describing his experiences perien ces he wrote that at the top of each ladder ladder he had to lie down and gasp with a wet bulb temperature exceeding about 80 degrees fahrenheit rise of body temperature is easily produced during muscular exertion particularly in a man encumbered cumb ered by a rescue apparatus unless the apparatus gives a very free supply of al air free from CO the effects on the breathing will be severely felt and in all probability excess of coa will produce unconsciousness much more readily than when there is no rise of body temperature in certain forms of rescue apparatus the supply to the breathing bag of air or oxygen free from CO coa is limited so that if the wearer is breathing a larger quantity of air he has to breathe re part of his expired air it will be seen at once from what has been said that the necessary result of this is a cor corresponding anding increase in the breathing and if the supply of pure air is not more than two or three times what a man at rest requires the result of any considerable muscular exertion will be loss of consciousness within two or three minutes cases have been seen where complete loss of consciousness has occurred from this cause within two minutes although the air in the breathing bag contained about 50 per cent of oxygen apparatus should be airtight air alg tight t A rescue apparatus should not only pro vide for a pro proper per supply of breathable air but it must also oe de practically airtight air tight it if it leaks outward the quantity of air in the bag may easily become insufficient for breathing if it leaks inwards or both inwards and outwards poisonous gases and particularly carbon monoxide may affect the wearer it seems essential that the tightness of an apparatus including that of any face piece or helmet belonging to it should be capable of being easily tested the apparatus ought also to incommode the wearer as little as possible particularly when lie he |
