question:  What caused the explosion that resulted in the loss of air on Freedom 19?
context: [Transcriber's Note: This etext was produced from Worlds of If Science Fiction, September 1962. Extensive research did not uncover any evidence that the U.S. copyright on this publication was renewed.] General Finogenov notified Major Winship that the underground blast was scheduled for the following morning. Major Winship, after receiving the message, discussed precautions with the three other Americans. Next morning, before the sunlight exploded, the four of them donned their space suits and went and sat outside the dome, waiting. Major Winship attempted unsuccessfully to communicate with Base Gagarin. "When?" "Boom—boom!" said Pinov. "He's done it deliberately," said Capt. Wilkins, the eldest of the four Americans. In the airless void of the moon, the blast itself would be silent. "I'll try again," Major Winship said and switched to the emergency channel. He crossed with the floating moon-motion to the airlock and entered, closing the door behind him. The darkness slowly filled with air, and the temperature inside the suit declined steadily. His foot was lifted for the second step when the floor beneath him rose and fell gently, pitching him forward, off balance. It then abated to something in excess of normal. Air currents whisked it away and plastered it against a riveted seam of the dome. It pulsed as though it were breathing and then it ruptured. Major Winship moved quickly to cut out the emergency air supply which had cut in automatically with the pressure drop. It's on your right side, midway up. Major Winship said, "they should have made these things more flexible." The sheet began slowly to slide downward, then it fell away completely and lay limply on the floor. "Just leave us alone, thank you," Major Winship said and cut off the communication. "I'll be damned surprised," Major Winship said, "if they got any seismic data out of that shot.... Squeezed in front of the massive transmitter, Capt. Wilkins had energized the circuits.
output:  The calking mixture leaked onto the air tank.
options:  The room became too hot from overcrowding  The calking mixture leaked onto the air tank.  The compound mixture became too hot because of the lack of the air reconditioner  The compound mixture was mixed too quickly.