During the second half of 1915 there were frequent occurrences of men descending to rescue comrades and themselves succumbing to carbon monoxide. Such rescue attempts in tunnels filled with carbon monoxide by men unprotected by breathing apparatus frequently led to more deaths. An example of many such incidents occurred at La Boisselle on 9 December 1915, when the British blew a charge against the 1st Reserve Company of the 13th Wurttemberg Pioneers. What followed was a nightmarish scene of frantic confusion. Georg Maier, a Pioneer on duty at the central listening post, had, immediately before the blow, descended a 15m shaft, a microphone apparently having detected British activity. His orders were to go to the tunnel face, where the particular microphone was located, to establish the direction of the sounds. He had only got about a metre along the tunnel when the explosion occurred, pinning him to the ground and collapsing the last 3m of the shaft behind him. Immediately after the explosion, Tunnel-Corporal Rubensdörfer arrived to ascertain the damage and, hearing Maier’s groans and cries for help, alerted men in the mine dugout at the tunnel entrance. Lance-Sergeant Dimmler took command and brought breathing apparatus and rescue equipment to the shaft and with the available men began to clear the damage to reach Maier. After a short time Lieutenant Stolze, the duty officer, took over and, while Dimmler continued in the shaft, divided all men between the shaft, operating the fans to clear the gas and as reliefs. With great difficulty they managed to get an air hose close to Georg Maier and, using a bellows, supply some fresh air to him. By 6.45pm, three and three-quarter hours after the blow, Lance-Sergeant Hämmerle and Corporal Jacob Maier squeezed through a hole to the injured man and found him trapped by the feet but alive. However, the gas soon forced the two men to leave the gallery and they were relieved by Pioneers Zimmermann and Schmiederer. Zimmerman worked at the face to free Georg Maier, but the gas forced him to leave after just ten minutes. Schmiederer continued enlarging the opening and, despite warnings, stayed in the gallery. Lieutenant Stolze was also forced to withdraw and his place was taken by Corporal Koch. Pioneer Fegert reached Schmiederer and managed to give the trapped man some alcohol, and he showed signs of life by groaning and catching his breath. Suddenly a white cloud of powerful fumes swept up the gallery and brought such an intense heat that Fegert and Schmiederer were forced to leave the injured Maier. The cause appears to have been a secondary explosion of gas, probably methane, released by the blow. Fegert squeezed back through the gap into the shaft and tried to pull Schmiederer through behind him, but Fegert collapsed and had to be pulled up the shaft, leaving Schmiederer unconscious at the opening. Corporal Koch also had to be pulled up, overcome with gas. Pioneers Kastler, Kieninger and Schulze descended the shaft, but Kastler and Kieninger immediately collapsed unconscious. Schulze called on Corporal Sieber to throw him down a harness as he had the unconscious Schmiederer in his arms. Sieber brought it down himself and placed it around Schmiederer, but by this time Schulze was also unconscious. Sieber was now himself on the verge of collapse and called for help, at which point Corporal Rehm descended and brought him to the surface. Rehm returned down with Pioneer Mohr, who tied a rope around one of the men and then ascended to pull him up. Rehm had now collapsed and Mohr went down again and brought him back up. Mohr returned with Pioneer Mauch, who brought the unconscious Schulze halfway up the shaft, from where Mohr helped. Mohr then collapsed, and Mauch had to let Schulze fall in order to save Mohr. He tied Mohr by the feet to the shaft rope and succeeded with the help of some other pioneers in hauling him out. Pioneers Blattner and Kakuschte now tried to rescue the men at the bottom of the shaft, but the fumes, coming more strongly from the gallery, showed that the tunnels were on fire. At 8am Lieutenant Stolze ordered that no one was to descend the shaft. As well as Georg Maier, Schmiederer, Kastler, Kieninger and Schulze perished.²⁴

The proper equipping and training of rescue teams went some way to preventing such unnecessary casualties. Mine gas was a recognized hazard in military mining well before 1914, but the apparatus used by the military had been superseded by civilian developments. The helmets fed by air-pumps such as the Applegarth Aérophore sent to France by the British in 1915 were found to be of little use. The demand was for self-contained re-breathing apparatus, in which the wearer carried on his person a cylinder of compressed air and a cartridge of sodium carbonate, which ‘scrubbed’ the carbon dioxide from exhaled air, which was saved in a rubberized bag. The wearer added air from the cylinder into the bag according to need. The Germans issued large numbers of the Dräger set, which lasted for half an hour, as they were also used to protect key infantry against poison gas employed on the surface, and in 1916 they introduced

a military version, the Army Foul Air Breathing Apparatus (HSS).