As investigators try to figure out what caused a house explosion in Pennsylvania that killed six people, their loved ones are reeling from the unimaginable loss.

The explosion in Plum, about 20 miles east of Pittsburgh, was so powerful that it all but leveled the home and started multiple fires at nearby houses. The cause is under investigation, though the homeowners had been having problems with their hot water tank, officials said Monday.

The homeowners, Heather and Paul Oravitz, were the only members of their family known to be inside at the time of the explosion. The four other victims are their neighbors.

Among those killed were a proud father who gave his daughter away at her wedding last month, a super involved hockey mom and dad who never missed a game, and a 12-year-old boy described as a "1,000% momma's boy."

Here's what USA TODAY has learned about them:

Heather and Paul Oravitz

Devoted parents who raised two great kids, Heather and Paul Oravitz were truly special people, said Melissa Campbell, a family friend who began a GoFundMe page for the children, who are 21 and 23 and miraculously were not in the home when the explosion happened.

"The sheer magnitude of the devastation, and the actual event itself, is rather incomprehensible," she said, adding that everyone who knows the Oravitz family is in shock. "When my mind goes to that place because it's so unexplainable, I try to focus back on my fond memories of the Oravitzes."

She recalled getting to know the couple over the years as their sons played in the Pittsburgh Penguins Elite AAA program, culminating in 2019 when the boys won the national championship.

Hockey parents travel all over for games, so they got to know each other well over the years.

"When you play at that level, you travel two or three weekends out of the month and you're on the road with these folks and they become your family," she said.

She said Paul, 56, and Heather, 51, were "very devoted, very family-focused, dependable and kind."

"They were someone you could laugh with and someone that would hug you when you needed support," Campbell said.

She said she started the GoFundMe for the couple's children, Cole and Taylor, as they struggle with the loss of their beloved parents and begin picking up the pieces of their lives.

Kevin Sebunia

Kevin Sebunia had just experienced one of most dads' biggest dreams: giving his daughter away at her wedding, according to a Facebook post written by his aunt, Carol Klauss.

The post included a photo of a beaming Sebunia dancing with the new bride at the July 1 wedding.

"We are devastated," she wrote. "This is a nightmare. It sounds like a cliche to say that Kevin was one of the very best guys we’ve ever known, but it is so true!"

An obituary posted on a funeral home's website says that friends jokingly referred to Sebunia as “Mr. Home Depot” because of his way with tools and his ability to fix things.

"If someone needed help, Kevin would reply, 'I’ve got a tool for that!' or 'I know a guy,' and he usually did," the post reads.

Sebunia enjoyed going on grand adventures with his wife of 32 years, Kelly Klauss Sebunia, with the couple recently conquering the challenging 24-mile hike from the Grand Canyon's North Rim down to the Colorado River and up the South Rim, according to her Facebook posts.

Other posts show the couple enjoying trips to Cabo San Lucas, Mexico and North Carolina's Topsail Island.

Claudia Lardizabal, who identified herself as a colleague of Sebunia's for 12 years, said on Facebook that "his girls meant the world to him."

He also adored his dog Harper, was an avid outdoorsman and a passionate cook known for his charcuterie boards, the obituary says.

"The world has lost a remarkable man who touched and impacted countless lives," it reads. "His passing has left a void in everyone’s hearts that can never be filled. He will be deeply missed by all who knew and loved him. Until we meet again ..."

Sebunia is survived by his wife, two daughters, and a grandson, among others.

Casey and Keegan Clontz

Casey Clontz and his 12-year-old son Keegan were just about inseparable, their loved ones told Pennsylvania's Tribune Live.

Jen Clontz, Casey's wife and Keegan's mom, told the newspaper that her husband was loving and that Keegan was a big brother to a twin sister and younger sister. He was also a devoted son who was pretty much his dad's shadow but also “1,000% his momma’s boy.”

Keegan played football for the Plum Mustangs and would have started junior high in a week and a half, the newspaper reported. Casey Clontz, 38, was a massive Pittsburgh Steelers fan and made sure everyone knew it, proudly tattooing his love of the team on his leg.

“Keegan and Casey were their most happy when they were spending time at the lake with their lake family and friends. They swam, did boating and loved cruising around in their golf cart,” their family said in a statement to Tribune Live. “Keegan and Casey will be missed by so many and will continue to be loved by so many, including their family, friends and community.”

A GoFundMe started for the family says that "they are just beginning to navigate this horrible tragedy."

"The road ahead for the family is and will continue to be long and hard," the post reads.

Michael Thomas

Michael Thomas, 57, also was a neighbor of the Oravitz family who was in the house when it exploded.

Tribune Live reported that neighbors attending a vigil for the victims on Tuesday described the corner where the house once stood as a "fraternity row" because everyone was friends and always spending time together.

Rafal Kolankowski told the newspaper that Thomas once came over to help when he was installing concrete steps in his front yard.

“Mike was a cool dude,” Kolankowski said. “If you needed something, he was there.”

Amanda Lee Myers covers trending news and human-interest stories for USA TODAY. Reach her at [email protected] or follow her on X @AmandaLeeUSAT.