 What caused the explosion that resulted in the loss of air on Freedom 19?
[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. The sun rose with its bright, silent clap of radiance. Black pools of shadows lay in harsh contrast, their edges drawn with geometric precision. Major Winship attempted unsuccessfully to communicate with Base Gagarin. "Help?" " Nyet ," said Major Winship, exhausting his Russian. When—boom?" "Is Pinov," came the reply. "When?" "Boom—boom!" said Pinov. "He's done it deliberately," said Capt. Wilkins, the eldest of the four Americans. One by one they clicked on their cooling systems. "Ah, it's all Russian. In the airless void of the moon, the blast itself would be silent. A moth's wing of dust would, perhaps, rise and settle beyond the horizon: no more. "I'll try again," Major Winship said and switched to the emergency channel. "Base Gagarin? Base Gagarin?" "Tell him, 'Help'," said Capt. Wilkins, "so he'll get somebody we can talk to." "I'll see them all in hell, first," Major Winship said. "Hell, Charlie, I feel stupid sitting out here," Capt. Lawler said. 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. At the proper moment of pressure, the inner lock slid open and Major Winship stepped into the illuminated central area. 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. "Well," Lt. Chandler commented, "even though we didn't build this thing to withstand a moonquake, it seems to have stood up all right." 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.
 The calking mixture leaked onto the air tank.
 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.