550 THE COLLIERY GUARDIAN. September 13, 1918. the apparatus more comfortable to wear when the feed is low. The greater comfort is partly due, it is claimed, to the less highly distended state of the breathing bag, and partly to the reduced temperature of the inhaled air. The latter effect can only result from a decrease in CO2 absorbed, and this again from a decrease in CO2 exhaled. There is only one way of reducing the volume of CO2 discharged by the body, and that is to do less physical work. In other words, by setting the oxygen feed at a low figure the amount of work it is possible to perform with the apparatus is restricted, and thus the temperature of the air is kept down. Obviously, it oughf not to be necessary to have recourse to such an expedient to make the air cool enough to breathe with comfort. The Proto apparatus, however, is particularly prone to overheating. Proto Apparatus: Automatic Relief Valve advocated. — The unpleasant degree of distension of the breathing bag which follows from a 2-litre oxygen supply during gallery work (much of which is light in character) is a complaint peculiar to users of the Proto apparatus. In the other types adopted in this country the relief valve opens automatically when the pressure within the apparatus reaches 4 in. of water, or there- abouts ; but the blow-off of the Proto is actuated by hand. The Committee believe that it would add to the comfort of the Proto apparatus, and remove one of the temptations of adjusting the oxygen feed too low, if the relief valve were made automatic in action. Owing to the presence of the caustic at the bottom of the bag, there is little fear of its being squeezed so flat that the wearer will be unable to draw breath. Constant Feed Apparatus: Minimum Feed Prescribed.— In view of the fact that rescue apparatus, if satisfactory, must be such as to enable a man to attempt hard work without risking oxygen starvation, the Committee advise, in the case of any breathing apparatus dependent on a uniform oxygen delivery, that it should be made illegal to adjust the reducing valve to supply less than 2 litres per minute. The report then refers to the death of Hugh Doorbar at the Podmore Hall Colliery disaster, and to Dr. Briggs’s examination of and conclusions with regard to the apparatus (see Colliery Guardian, February 22,1918, p. 383). The Injector. In the Draeger and Meco apparatus the circulation of • air is induced by an injector. This gives a constant flow independent of the breathing, but limited in amount. With the helmet an arrangement of this kind was practically a necessity on account of the large space in the helmet, and the hopelessly impure nature of the air which would occupy that space but for the clearing effect of a current independent of the lungs. As has already been pointed out, however, this was at best a dangerously inadequate makeshift, since, during considerable exertion, the circulatory volume was quite insufficient. With the abolition of the helmet the need for the injector disappears, as the lungs themselves can now provide perfectly for the air circulation. Indeed, in mouthpiece apparatus the injector exists as a “ vestigial structure ” and, as is often the case with such survivals, it is responsible for more risks than benefits. It has been claimed as an advantage of the injector that there is cooling of the air as it passes the injector, owing to the expansion of the oxygen as it leaves the nozzle. This effect is actually present, but is quite small in magnitude. An injector which was adequate in all circumstances, and which never got out of order, would be able to make breathing a little freer; but the idea that it would be of great advantage appears to rest on imperfect physio- logical knowledge. The lungs are so controlled that they are able easily to deal with the very moderate resistance of a properly designed purifier circuit. When that resistance is encountered the respiratory muscles act more powerfully, so that the amount of air breathed is just as great as without the resistance, both the volume of air breathed and the force and depth of expiration being regulated by the percentage of C02 in the air of the lungs. With existing injectors the whole physio- logical object of breathing is defeated as soon as the volume of air breathed becomes greater than that circulated by the injector; and the result of this is often most dangerous. Negative Pressure.—The injector is liable to create a. negative pressure behind it, the effect of which is to cause an inflow from the outer atmosphere if there should be a leak in the negative pressure zone. One death has resulted from this cause.* By altering the position of the injector Draeger has, in a more recent design, succeeded in placing the absorption cartridge in the positive pressure part of the circuit.f This is an improvement; it considerably reduces, but does not entirely remove the danger in question. A variant of the Meco apparatus, known as the “ positive pressure ” type, is also on the market.^ In this form an auxiliary bag is introduced, at the back of the wearer, and in connection with the metal-cooling pipe leading to the injector. No dependence can be placed on this arrange- ment as ensuring positive pressure. The auxiliary bag only acts as a rough kind of pressure indicator. When distended—which, in actual use, is seldom—there is certainly positive pressure throughout the circuit; but its distention cannot be observed by the wearer, nor have we ever met a trained man claiming to be able to feel the distension through his clothing. To place a bag—of all things the one most liable to leakage—in the very part of the circuit where leakage is most likely to have fatal.results, is adding to the danger instead of diminishing it, and such a bag should never be used. Risks of Insufficient Circulation.—If the flow were always maintained, and if the purifier always acted perfectly, 50 to 60 litres of pure air per minute would be ample for the most exacting work tbe wearer is * Prof. J. Cadman: “ Mine Rescue Appliances. A Danger Occurring in the Use of Apparatus in which an Injector is Employed.” Trans. I.M.E, xliv., p. 463. t British Patent No. 4378. 1913. j Trans. I.M.E. xlv., p. 230. likely to be called upon to perform with rescue appa- ratus; but if it should sink to, say, 35 litres, as has often been observed, it becomes insufficient for hard exercise. The circulation may fall to the vicinity of the latter figure owing to incorrect setting of the reducing valve, to the partial clogging of the secondary nozzle, to leakage from the circuit, to the accumulation of water or other material in the pipes, or to an increase in the resistance of the purifier. Even though it may prove up to standard at the start, the circulation usually diminishes—and sometimes diminishes considerably— during a practice. Had one been dealing with pure air the problem would resolve itself into getting some effectual guarantee that the circulation never fell below a stipulated figure, say, 45 litres per minute; but it is unfortunately complicated by the influence of CO2 upon the tidal volume demanded by the lungs. This influence is so marked that an air circulation which is enough when the air is pure easily becomes insufficient when the cartridge begins to fail. When the wearer of an injector apparatus fitted with inspiration and expiration valves requires a greater air- volume than the injector supplies he exhausts the inspiratory bag and overfills the expiratory bag; breathing becomes more difficult, until eventually the inspiratory bag flattens in mid-breath. The sensation of the lungs being checked in this manner is extremely distressing and is apt to produce panic, and such an occurrence has to be prevented at all hazards. The Meco and Draeger appliances must now be examined to see how they guard against this danger of an over-driven apparatus. The former attains its object by omitting both inspiratory and expiratory valves, thus putting on the injector all the responsibility of main- taining the flow. The bag on the exhalation side cannot now be overfilled at the expense of that on the inhalation side, there being nothing to prevent a readjustment of pressure between them by back-surging of the air. Even if overdriven, breathing can goon, the lungs being partially filled by exhaled air reinhaled. In most of the patterns of Draeger apparatus used in this country the two compartments of the breathing bag are connected together by a narrow passage. Provided the pressure in the inhalation compartment exceeds that in the exhalation compartment (which is the normal case), the flow in this passage is in parallel with that going to the lungs; but when the apparatus is overdriven the pressure in the exhalation bag becomes the greater, and some air from that bag returns through the passage to prevent the inhalation compartment being sucked flat. In another Draeger design the passage between the bags is omitted but the expiratory valve is left out, thus allowing the lungs to fill themselves from the exhalation bag if the circulation is insufficient. We look upon these expedients with the gravest suspicion. All three of them are alike in that unpuri- fied air is used to make up the indrawn volume when the lungs’ demand exceeds the injector’s supply. Con- sider what happens with an apparatus of this kind if provided with an inadequate purifier. As soon as the cartridge begins passing CO2 the breathing automati- cally intensifies; a greater proportion of the volume in circulation passes into the lungs and the air delivered to the cartridge becomes richer in CO2. These effects become more and more marked until the lungs need more than the injector can supply. At this critical point relief is given by adding expired ah’ to air already dangerously charged with CO2, with the result that the moment of complete failure approaches at an accele- rating rate and unconsciousness may rapidly supervene. The elimination of both valves in the Meco apparatus has the same effect as a large dead space, for even with gentle exercise the lungs send back a part of the expired volume into the inspiratory bag, from which it passes to the wearer on the next inhalation. Similarly, with that type of Draeger in which the expiratory valve is omitted, an indrawn breath is always more or less polluted with, vitiated air drawn back from the expiratory bag. These two latter methods of preventing tbe inhalation bag f>eing sucked flat are particularly objectionable; at one and the same time they reduce the margin of £ safety and the amount of exertion possible to the wearer. N o injector contrivance is safe from the serious danger under discussion unless it is so arranged that the lungs can at all times get the volume they require without having to draw upon unpurified air. Both inspiratory and expiratory valves must be present, and it must be made impossible for any air to reach the lungs without having first been through the purifier. Injector Apparatus: Risk of withdrawing Mouth- piece.—If a man wearing an apparatus should trip and fall—as he is particularly liable to do when walking in smoke—his mouthpiece may be knocked out, and it may be a few moments before he recovers himself sufficiently to get it back again, or—in a more serious case—before his comrades can do so. Mr. J. H. Thorne, of the Forth Rescue Station, called our attention to a third drawback of injector apparatus, namely, that if the mouthpiece be withdrawn the injector will suck some of the outside air into the apparatus. Such a risk, certainly, does not exist with lung- operated apparatus, like the Proto or Weg, where the removal of the mouthpiece merely causes an outflow from the bag until atmospheric pressure is restored. In order to ascertain the extent of the danger in question, a Meco apparatus was placed with its open mouthpiece in an atmosphere containing 2’73 per cent, of carbon monoxide, samples being drawn from a tap on the inhalation tube at intervals of one, two, and four minutes after starting the oxygen supply. These samples respectively analysed 0’30, 036 and 0 41 per cent, of carbon monoxide, indicating a serious contami- nation of the air within the apparatus. Choking of Injector.—The injector suffers from a further drawback in its liability to become choked. Most instructors at Meco and Draeger stations—parti- cularly at the former—have experienced this trouble, and if it occurred in irrespirable air the result would probably be fatal. The secondary nozzle and openings thereto occasionally get choked with dirt or caustic particles carried along the air passages. While inter- fering with the efficiency of the injector as a pump, such an occurrence rarely checks the oxygen feed. When the inner nozzle is blocked, on the other hand, the material obstructing the passage is generally found to have come from the reducing valve side. A very small particle is enough to stop the hole. A case is on record* of a nozzle becoming completely blocked during use by a minute piece of metal from a gauze. The wearer of the appa- ratus fell unconscious. To prevent rust particles and other small fragments entering the nozzle from the pressure side, a filter is interposed between the injector and the reducing valve. In the Draeger apparatus the filter is a disc of very fine gauze, the openings in which (measured by means of a microscope having a micrometer eyepiece) are 1/12 mm. square. The mesh is thus sufficiently fine to catch anything that could block the nozzle. The Meco apparatus, when correctly fitted, possesses a filter consisting of a tight plug of cotton wool, held between two gauzes and clamped firmly in place. This, again, is efficient. But there are at rescue stations a consider- able number of Meco apparatus in which the plug has been omitted though the gauze discs are present. Now the average Meco nozzle is 0’3 mm. in diameter, while the gauze mesh measures 0’2 mm. in the clear. This apparent margin of safety, however, may not actually exist, as the microscope shows that the drill has not always left a clean hole, and that the actual orifice of the jet may be half-moon shaped or quite irregular. The following measurements relate to five Meco nozzles selected at random:— (1) Half-moon shaped orifice; maximum width, 0’23 mm.; minimum width, 0’17 mm. (2) Clean round hole, 0’28 mm. diameter. (3) Clean round hole, 0’37 mm. diameter. (4) Irregular orifice, maximum width, 0’25 mm.; minimum width, 0’20 mm. (5) Clean round hole. 0’35 mm. diameter. If it is borne in mind that the filter could not stop anything less than 0 2 mm., the highly dangerous nature of jets (1) and (4) is evident. It must not be inferred that by removing the injector all chance of choking the oxygen supply is eradicated. That possibility exists with apparatus such as the Proto, which has no injector, but which, nevertheless, has a fine opening on the discharge side of the reducing valve. Of the two, however, the injector is more liable to choke; the orifice is longer and is smaller in bore. Recommendations Relating to Injector.—There is no gainsaying the fact that the injector, as an adjunct to breathing apparatus, is a grave source of danger. To do away with it entirely is the only satisfactory solution of the problems to which it gives rise. We recommend that it be abolished in all future rescue apparatus, and that existing apparatus be altered, as soon as practicable, to eliminate the injector. (To be continued.) * South Midland Report, p 45. FIRING WET HOLES/4 By T. F. Price. The accompanying illustration shows a method that has been used quite successfully in firing wet holes. A is a stick of dynamite, B is the detonator and C is a paraffin seal. In preparing this cartridge the covering on the end of the stick of dynamite is first opened care- fully. Next, with a stick of suitable size, a hole is made in the explosive to a depth equal to at least twice the length of the detonator. The fuse should now be trimmed in order to be sure that the end entering the cap is perfectly dry. This Method of Firing Wet Holes. end is next inserted and the detonator carefully crimped. The paraffin is now applied, being carefully pressed firmly around the cap and fuse. For this purpose, the paraffin may be brought to the proper consistency by kneading and working in the hand. The detonator may now be inserted in the cartridge, the wrapping being securely tied around the fuse. The other end of the fuse, as shown at E, should now be split, exposing the core e. When the charge of explo- sive is properly put in place and tamped, all that now remains to be done is to light this core e and retire to a safe distance. This method has been repeatedly used when firing charges submerged under 15 ft. of water, with uniformly good success. * Coal Age. Yorkshire Miners’ Association. — Mr. Herbert Smith, president of the Yorkshire Miners’ Association, speaking at a meeting of the executive on- Tuesday at Barnsley, said that the miners were doing all they could to increase the output of coal, but they had received complaints of unfair treatment by some coal owners, and unless that was altered they could not increase the output. In his opinion there was a dead set by some collieries against the Coal Controller. Jf that were so he could understand men being victimised. The Coal Controller and the Presi- dent of the Board of Trade were warned when the last two comb-outs took place that they would have to face a serious position if the men were taken. They were not strong enough, however, to resist the Minister of National Service, and they allowed the men to go. Unless men were returned from the Army apart from B 2 or B 3 men, he was afraid they would not be able to make much headway, though they would do all they possibly could to increase the output.