These are the challenges that rescuers face in the building that collapsed in Miami

(CNN) – For the sixth day, search and rescue teams meticulously made their way through piles of rubble after the building collapsed in Surfside, Florida, in hopes of finding more survivors.

As of Tuesday night, at least 12 people had died and 149 people were missing, authorities said.

“We are moving debris piece by piece and searching,” Miami-Dade Fire Chief Alan Cominsky said Tuesday, describing what he called a “tedious process.”

Teams from across the state have helped. The US Federal Emergency Management Agency (FEMA) has dispatched aid, and teams from Israel and Mexico are helping as well.

These are some of the challenges that rescue teams face.

The rubble is falling

The pieces of concrete the teams are grappling with are the size of basketballs and baseballs, Raide Jadallah, Miami-Dade Fire Rescue assistant chief of fire operations, said Monday.

Miami-Dade County Mayor Daniella Levine Cava said Friday that debris falls on crews at the site as they do their work.

“We have structural engineers on site to make sure they don’t get injured, but they are proceeding because they are highly motivated,” added Levine Cava.

The rubble is moving too

Overnight through Tuesday, debris fell from parts of the building that remain, Surfside Mayor Charles Burkett said.

And workers were moving away from a “13-meter area to the side of the building” due to concerns about debris protruding from the standing part, Cominsky said.

The west side had to be cordoned off “because it was getting excessively dangerous to work there,” Burkett said.

The pile of debris moves as crews work, authorities said.

“The current situation is that we are not lifting floor by floor,” said Jadallah. “We are talking about concrete. We are talking about steel. Every time there is an action, there is a reaction.

He said that on Sunday, as crews looked through the rubble, a rescue worker fell 7 meters down the pile of the collapsed building.

“That is a perfect example of the situation we are facing. This was, again, witnessed by the family members themselves on the site, ”he said. “It’s not that we can connect a pair of cables to a concrete rock, lift it up, and finish.”

There is a lot of debris to move

The building was 12 stories high. So far, crews have moved about 3 million pounds of concrete, Kominsky said Tuesday. “That is more than 24 cubic meters,” he said.

As crews searched for empty spaces in the rubble where survivors might be digging from below, heavy machinery has been lifting pieces from above.

But the people who slept in their rooms when the building collapsed “are under four or five meters of concrete,” Col. Golan Vach, commander of Israel’s National Rescue Unit, who is helping with CNN, told Wolf Blitzer on Tuesday. the search.

“So this is what they are doing now, penetrating the concrete,” Vach said.

Vach said that of all the places he’s done similar work – Turkey, Haiti, Albania and Mexico, for example – this site is the most difficult because of the way the building collapsed on itself.

Jadallah stressed that the process “will take time.”

“It is not going to happen overnight,” Jadallah said. “It is a 12-story building. It’s going to take some time.

Some fires broke out at the site

When some fires broke out at the site over the weekend, crews had to work to get it under control and control the smoke.

Levine Cava said Saturday that progress had been made with fire and smoke hampering the search effort.

Wind and rain can make rescue more dangerous

It’s the rainy season in Florida, and the wind and rain only made the situation even more dangerous, authorities said.

Some work had to be stopped at times due to lightning.

On Sunday, Burkett said rescuers’ fortunes “seemed to change” when it came to the fires and the weather.

Now, he said, “we just need a few more miracles every day.”

CNN’s Amanda Watts, Eliott C. McLaughlin, Steve Almasy and Elise Hammond contributed to this report.