Two men who were injured in a hash oil explosion that destroyed a Walnut Creek apartment on Halloween remain hospitalized in critical condition, a fire official said Wednesday.

Fire Marshal Robert Marshall of the Contra Costa County Fire Protection District said that while the men are still listed in critical condition, medical providers are now “a little more optimistic about their survival.”

The two were injured in an explosion at an apartment within a complex in the 1500 block of Sunnyvale Avenue around 10 a.m. Friday, according to fire officials. Both victims were airlifted to the University of California at Davis’s Burn Center in Sacramento.

A neighbor was also treated for minor injuries suffered in the blast. Fire officials said the explosion and fire left the six-unit apartment complex uninhabitable, displacing an undisclosed number of residents.

The American Red Cross set up a shelter on Friday for the displaced residents. Police and fire investigators continue to investigate the explosion, which resulted from a marijuana and hash oil drug extraction manufacturing process, according to police.

Anyone with information about the explosion and fire is asked to call Walnut Creek