Fire officials said the propane tank leak at the Logan Township Municipal Building construction site this morning was caused by a safety valve that was frozen open.
The leak occurred when a 1,000-gallon tank of liquid propane being moved across a parking lot rolled onto a nest of valves, breaking one, according to Altoona Fire Chief Reynold D. Santone Jr.
Normally when a valve breaks, the rush of propane boiling out of the valve would activate an emergency shutoff plunger within the valve to seal against a seat, preventing leakage, said Jeff Shaffer, president of the Pennsylvania Propane Gas Association.
But in this case, moisture or some other contaminant on the safety shutoff froze the plunger open due to the intense cold generated by the released propane as it turned from liquid to gas, according to Deputy Fire Chief Tim Hileman.
Officials worried that the propane, which is heavier than air, would travel into nearby neighborhoods where a spark could have touched off an explosion
Students from neighboring Pleasant Valley Elementary School were initially taken to Altoona Area High School but then transported back to their own school before 10 this morning when the area was deemed safe, according to Altoona Area School District spokesman Tom Bradley.
Students at Bishop Guilfoyle High School were shifted from the back of the school to the front, which is farthest from the construction site, according to acting principal Timothy Lucko.
Nearby residents were initially told to stay in their homes by officials, after readings determined the gas was not in an explosive concentration.
Mirror reporters are working on a story for Thursday's paper.
