But during times of extra exertion a man needs more air than at others, for which provision has to be made, and so on his chest the rescuer carries a flexible bag divided into two compartments. Through one of these the exhaled air passes on its way to the regenerator, while through the other the oxygenated air flows on its way to the man's mouth. When he is breathing hard, then, during a moment of extra exertion, and when, therefore, he is turning out bad air faster than it can be purified, and drawing in pure air faster than it can be produced, this bag comes to his aid. From the store of oxygenated air in one side of it he draws the extra which he requires, while the other side stores up temporarily the excess of vitiated air, until the regenerator is able to overtake its work. Thus at all times, whether breathing ordinarily or heavily, the apparatus can respond to his demands.
The spray of oxygen as it escapes from the cylinders into the injector has the effect of driving the air along, so that the circulation through the tubes and the regenerator is automatic, and the foul air flows away from the man's mouth and the new air comes back to him quite without effort on his part. As time goes on, of course, and the stored oxygen becomes used up, the pressure in the cylinders falls, which fall, shown upon a little pressure-gauge, tells the man how much longer time he has before he must return for fresh supplies of oxygen and soda. Fresh cylinders of oxygen can be connected up very quickly in place of the empty ones, while a fresh regenerator can be put in, or new caustic soda supplied, in a very short time.
The superintendent of the Mansfield station has invented what is termed a "self-rescue" apparatus, to be used in conjunction with that which has been described above. It is simpler and lighter than the rescue apparatus, and will not keep a man supplied with air for more than an hour or an hour and a quarter. Moreover, it is not automatic, since the flow of oxygen has to be controlled by the man himself. Since, however, it consists only of a mouth-piece, a breathing-bag and a cylinder of oxygen, it is very portable, and may well be carried by a rescue party for the use of any men who may be discovered alive beyond the danger zone. It may well happen, indeed it often has happened, that a remote part of a mine, although cut off from the shaft by passages full of "after-damp," as the foul gases caused by the explosion are termed, may itself contain fairly pure air in which men can live for a long time. If such men be reached, the difficulty is to get them through the passages containing the bad air. Consequently a rescue party which carried one or two of these light forms of apparatus could equip such men with them and then they could pass out with safety.
Another use, the one, in fact, from which the appliance draws its name, is the facility with which, by its aid, a man could set right a chance defect in his ordinary rescue apparatus. Suppose, for example, that a fully equipped man found something wrong, whereby he was prevented from getting his proper supply of purified air. Then, if the party had one of the self-rescue sets with them, he could slip off his helmet or mouth-piece, quickly replacing it, for a time, with the self-rescue mouth-piece. This might enable him to reach safety, or even to put the other apparatus right and then don it once more. The whole thing can be packed up into a small tin case which can be slung over one shoulder, and with the oxygen cylinder slung over the other one the complete outfit can be carried quite easily by a man in addition to what he is wearing himself.
Still another form of breathing appliance may well be taken on these rescue expeditions, and that is the reviving apparatus, for use upon those who have apparently ceased to breathe. In this case a mask is put over the sufferer's mouth and nose, and then the turning of a lever into a certain position causes oxygen to escape from a cylinder in such a way as to cause a suction which empties the man's lungs of the bad gases which have laid him low. That done, another movement of the lever and a deep breath of oxygen flows into his lungs in their place. Thus by alternating the positions of the lever an artificial respiration is set up far more effective than can possibly be attained by the ordinary method of moving the man's arms and pressing his chest. Indeed there are cases, such as when his arms or ribs are injured, when the ordinary method is impossible, but it is hard to imagine an instance when this beneficent apparatus could not be used, and so long as there be any spark of life left in the poor fellow there seems to be every reason to expect a complete revival as the result of its use.
Of course there are many other places where poisonous gases are likely to be met with, such as gas-works, chemical-works, limeworks, and so on, where this apparatus may be kept with advantage, in case of accident.
Indeed all that has been described above has its use apart from colliery explosions, although they are the outstanding opportunities for its employment. Old workings, tunnels which have been empty for a time, sewers—all these have, on occasion, to be entered, not to mention houses full of smoke, or factories full of chemical fumes, all of which form cases in which the rescue apparatus would find useful employment.