The concentration is less than in the case of Reactor 1 pipe (63%), as it was only 6.5%.
From Yomiuri Shinbun (10/12/2011):
TEPCO announced on October 12 that the high concentration of hydrogen gas was detected from the pipe that connects to the Containment Vessel of Reactor 2 at Fukushima I Nuclear Power Plant.
The concentration was 6.5%, lower than 63% detected in the pipe in Reactor 1 the other day. Nonetheless, TEPCO says "Normally the concentration of hydrogen gas within the Containment Vessel is less than 1%. The concentration detected in the pipe is higher than expected". It is likely that hydrogen gas generated right after the accident remains in the pipe.
TEPCO plans to install a gas management system to filter out radioactive materials in the gas inside the Containment Vessel. After the installation TEPCO plans to remove hydrogen gas. If there are more than 4% hydrogen and more than 5% oxygen in the atmosphere, a chance of explosion increases.
After the installation?
However, looking at TEPCO's diagram (from press handout on 10/12/2011), this pipe is different from the one they found 63% concentration in Reactor 1. The Reactor 1 pipe was originally used for the core spray system - i.e. it was a pipe for water, so were the valves. But the Reactor 2 pipe and valves on the pipe are for the flammable gas, which I suspect has different specs.
It looks like the ever-incurious TEPCO decided to use the pipe for gas in Reactor 2, probably correctly assuming the valves would stop hydrogen gas from the CV better than the valves for the core spray system.