YELLOWKNIFE - The Yellowknife fire department is trying to determine the cause of two recent house fires.

Darcy Hernblad, deputy fire chief of operations, said that the Borden Drive fire that occurred on the morning of April 20 has proven to be a difficult investigation.

"We were able to determine that the fire was started under the deck," Hernblad said, adding they are still unsure what caused the blaze.

Jennifer Pagonis, a neighbour, called in the fire and told the Yellowknifer she thought it was originally just a deck fire.

"It went from what looked like a small deck fire to the whole (back) of the trailer," Pagonis said.

Hernblad said that the damage was so extensive that the fire department was unable to determine the cause.

"We can't say that we feel it was this, or we feel it was that," Hernblad said.

He added that they do not know if the fire was set intentionally or accidentally.

On April 5, Serge Mercier's trailer 20 km outside of Yellowknife on Highway 3 caught fire.

The fire department arrived on scene to discover the trailer ablaze and set-up to fight the fire.

Hernblad said that the plan quickly changed.

"When the officer made the assessment he noticed a 400-pound propane tank," Hernblad said.

This meant that the fire department had to stand back and wait until it was safe.

When the fire retreated, fire fighters were able to spray water on the propane tank.

Fire Marshal Stephen Moss said "that the damage is so extensive," that any investigation is very difficult.