Four people were injured, including two seriously, late Thursday night in an explosion at a natural gas factory in an industrial zone on the outskirts of Jerusalem, police said. By Friday noon, the fire was contained but gas was still leaking and still in danger of igniting. The cause of the late-night blast in the Atarot industrial zone just north of the capital was initially thought to be a technical malfunction, police said, but on Friday Israel Radio reported that a truck carrying a gas canister backed into a fence. A spark ignited the canister on the truck and this caused other, stationary canisters in the factory to ignite. A factory worker was missing late Thursday night and rescue workers were concerned he was trapped in the burning building. Firefighters were working frantically to extinguish the blaze and blocked rescue workers' access to the factory amid concerns of additional explosions. The factory was badly damaged by the blast. The injured workers were rushed by Magen David Adom paramedics to Hadassah University Hospital at Ein Kerem. They were suffering from burns and smoke inhalation.