Asharq al-Awsat, quoted by Palestine Today, is saying that the four Gazans killed last week in a smuggling tunnel were victims of a tunnel collapse, not the "poison gas" that Hamas claimed.
According to the article, the smuggling tunnel was built by a member of Hamas two years ago, to bring in building materials. A crack developed in the tunnel so the owner hired ten men to repair it. During the repairs, the tunnel collapsed.
The owner, not wanting to pay compensation to the families of the dead, started a rumor through his Hamas circles that they died from poison gas that came from Egypt. Hamas seized on this idea to pressure Egypt and Hamas then transported the victims to the Al Najjar hospital, where the group demanded that the head of surgery issue a statement that they were killed from toxic gas.
He refused, but his statement under pressure mentioned that there might have been a gas explosion in the tunnel, allowing Hamas to make their accusations.