(CNN)The arduous search for a missing technology executive and five others feared dead after a suspicious fire destroyed a mansion in Annapolis, Maryland, could take days, fire officials said Tuesday. 

The 16,000-square-foot waterfront house belonged to executive Don Pyle, chief operating officer for ScienceLogic, company spokesman Antonio Piraino said. 

Pyle was believed to have been at home with his wife, Sandy, and four grandchildren. 

The sheer size of the structure and the fact that three-fourths of the building had collapsed into the basement, with piles of deep-seeded debris still smoldering, compounded the search, said Anne Arundel County Fire Capt. Robert Howarth, who is leading the investigation along with a team from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives. 

"Your looking at five standard houses put together," he said. "This is more of commercial fire than it is a residential fire. There are a lot of businesses that aren't 16,000 square feet. That adds to it." 

Pyle had not been heard from on Monday, and his colleagues at ScienceLogic were "hoping for a miracle," CNN affiliate WJLA-TV in Washington reported. 

By midday Tuesday, fire officials had not been able to search the still-burning ruins, Howarth said. Heavy equipment is being moved in over the next 12 hours to aid in the search for victims and clues -- a process that could take days. 

"We have some very unique challenges with this house," Howarth said. "The construction of the house contained a lot of very heavy materials. We're looking at some steel beams that weigh in the area of 7 tons." 
What was his wife Sandy's occupation?
unknown