HOUSTON (CNN) — When Joshua Gandara heard his cousin, Houston firefighter Robert Beebe, had died suddenly, he instinctively knew why.
"I knew (he was) saving somebody," Gandara said. "That's him ... He always put people first, before him. Anybody's needs before his needs."
Relatives of the 41-year-old Beebe -- including his parents, sister and nieces -- are not alone in their mourning. Four Houston firefighters, total, died when a wall collapsed during a major blaze Friday at a hotel.
There was Matthew Renaud, a 35-year-old who worked out of five stations in the 12 years he was with the Houston Fire Department. Robert Garner, 29, had been at Fire Station 68 since joining the department in October 2010. The youngest victim was Anne Sullivan, a 24-year-old who graduated from the city's firefighter academy in April.
"She had a whole career and her whole life ahead of her," Houston fire Capt. Ruy Lozano said of Sullivan.
The five-alarm blaze began in the Bhojan Vegetarian Indian Cuisine restaurant and spread to the adjacent Southwest Inn, which are in the southwest part of Houston along the Southwest Freeway.
City fire Chief Terry Garrison explained Friday that some of the more than 150 firefighters responding to blaze went inside the structure "because we thought we had some civilians in the structure."
"Unfortunately, the building had much more fire in it than we originally thought," he said. "The structure collapsed ... and our members who were trying to save lives were trapped."
Fellow firefighters quickly sprang into action, some digging through the rubble to get to their colleagues. Garrison said the death toll could have been much higher if not for their bravery and quick action.
"(There were) dozens and dozens of acts of courage that took place in the seconds when that wall came in," he said.
Fourteen other firefighters hurt in the incident -- including one in critical condition and another set to undergo surgery Saturday -- have been or are still being treated at local hospitals.
Luzano told CNN there are "a multitude of situations going on" related to their ailments, from heat exhaustion to injuries to their legs and more.
With the total number of casualties, Houston Mayor Annise Parker said Friday will "go down ... as the worst day in the history of the Houston Fire Department."
Members of the department, which is the third-biggest in the nation, are leaning on each other to get over the loss of their colleagues.
"We're one of the biggest families you'll ever meet," Luzon said. "We're very close... We take pride in having a little city attitude in a big city."
Authorities have not yet determined the cause of the blaze. Members of the federal Bureau of Alcohol, Tobacco, Firearms and Explosives were at the site on Saturday, as were members of the State Fire Marshal's office.
Assistant State Fire Marshal Kelly Kistner told CNN that 18 Texas firefighters have died on duty so far this year, including 10 first responders killed in an explosion at a fertilizer distribution facility in West, Texas.
To put this number into context, 83 firefighters were killed on the job nationwide all of last year, the U.S. Fire Administration reported.
Already, more Texas firefighters have died in 2013 than over the past five years combined, according to Kistner.
CNN's Sara Ganim reported from Houston, and CNN's Greg Botelho wrote and reported from Atlanta. CNN's Ryan Rios contributed to this report.