The horrific 1942 explosion at the Lehigh Portland Cement plant in Sandts Eddy killed 31 workers and could be heard from as far away as Camden, N.J. (FILE PHOTO, THE MORNING CALL)

The Lehigh Valley’s worst industrial accident took place a little over 80 years ago, when 20 tons of dynamite exploded prematurely at a limestone quarry in Lower Mount Bethel Township, killing 31 workers.

What caused the incident on March 26, 1942 at Lehigh Portland Cement Co.’s Sandts Eddy quarry was never fully solved, but there was speculation that unstable blasting caps set off the equivalent of 4,000 sticks of TNT, or enough to blast loose 120,000 tons of solid rock.

The blast was felt or heard up to 100 miles away, and it blew out windows as far away as downtown Allentown. The tragedy left 18 widows and 63 fatherless children.

On Sunday, the 31st Annual Lehigh Valley Workers Memorial will remember the Sandts Eddy tragedy. First held in 1991, the ceremony is meant to bring awareness to workplace safety and remember those who died from accidents or diseases caught at the workplace.

This year’s ceremony will take place at 1 p.m. at the Bethlehem Rose Gardens. To date, the Lehigh Valley Workers’ Memorial has identified more than 3,600 workplace deaths dating back to 1771, and will add five more names from the past year.

Former state Rep. Rich Grucela, who grew up near Sandts Eddy in Martins Creek, will present a history of the disaster.

“I think it’s important that we’re recalling it here as the 80th anniversary comes up,” Grucela said. “Especially so the younger people can understand the history of these workers that built this country, the cement workers, steel workers, the garment workers.”

John Werkheiser, a vice president for the Lehigh Valley Labor Council and chairman of the Workers Memorial, said the disaster was beneath the organization’s radar for years, but a campaign to build a memorial to the victims kept the memory alive.

“And through all the research that we thought we had done, up until — I want to say about maybe seven or eight years ago — we didn’t even know about it,” Werkheiser said. “We didn’t even have the names or anything, it just kind of slipped through. And you know, when 31 people died in one disaster, we were astonished that we didn’t catch this.”

A memorial to the 31 workers killed in an explosion at Lehigh Portland's Sandts Eddy quarry was built in 2016. (Evan Jones/The Morning Call)

The memorial was built at Church Hill Cemetery in Lower Mount Bethel in 2016 after a two-year campaign led by Ed Pany, creator and curator of the Atlas Cement Memorial Museum in Northampton; Grucela, and Morning Call columnist Bill White.

Pany, who spent years researching the cement industry in the Lehigh Valley, said the disaster hit the community hard.

“The church there had three or four services for the deceased because there were so many deaths, they couldn’t have one service,” Pany said. “So they had multiple services. You had brothers who had died. You had cousins. I mean, it was just a terrible, terrible tragedy because they were a close-knit group of local people.”

Portland cement has been produced since 1872 and was named after limestone from Portland, England, which was considered to be more durable than natural cement. It was created from a mixture of clay-like limestone and other materials cooked in kilns under very high heat. Sandts Eddy, like many Lehigh Valley locations, sits on top of a cement rock formation.

Founded in 1897, the Lehigh Portland Cement Co. had grown to be one of the largest cement companies in the Valley by the 1940s. A plant in Sandts Eddy, first operated by Quaker Cement Co., opened in 1911 and was acquired by Lehigh Portland in 1926.

The quarry itself was northwest of the town, about a mile away. It was 135 feet deep and its face was 680 feet long.

In an article published in The Morning Call for the 50th anniversary in 1992, reporter Frank Whelan described the process of blasting large chunks of the rock off the quarry’s face. Dozens of drill holes were placed about 10-to-15 feet behind the quarry and filled with explosives.

“A blast at the Sandts Eddy quarry in 1939 using 14 tons of dynamite was photographed by The Morning Call. It tore away 90,000 tons of cement rock along a 360-foot strip of the quarry face,” the article said.

The accident happened around 9:15 a.m. March 26, 1942, when some workers had just taken a break for a mid-morning snack. Lunch boxes were open. About 20 tons of dynamite had arrived from the Hercules Powder plant at Belvidere, New Jersey.

Some of the explosives were already placed in the drill holes. State experts later concluded that the crew was placing the dynamite in hole No. 33 at the time of the blast.

The names of the workers killed in an explosion at Lehigh Portland's Sandts Eddy quarry on March 26, 1942. (Evan Jones/The Morning Call)

The explosion came without warning as all 20 tons of TNT went up all at once. A sheet of flame swept over the quarry, killing all in its path. Bodies of quarry workers were ripped limb by limb or incinerated beyond recognition. A car parked nearby melted into a metal mass.

A nearby elementary school was in session that morning and at least one student had to be transported to Easton Hospital because he was hit by shards of broken glass. Farmer George Taylor of Mud Run, three quarters of a mile away from the blast site, was knocked off his tractor.

Further away from the blast, many were afraid there was a major accident at Bethlehem Steel. Word from Sandts Eddy didn’t get out until workers from Bell Telephone Co., who were dismantling a line 1½ miles away and were knocked off their feet by the explosion, found a nearby house and called for help.

When first responders arrived from Easton and Nazareth, there wasn’t much they could do. All they found were mangled bodies and “a leg here, or an arm there,” according to news reports.

“A number of years ago, I gave a speech when a lady came up and said she found a very worn shoe and an ankle bone in the shoe miles away from the site of Martins Creek while they were walking,” Pany said. “So whenever you get over a lot of memories of what people did or where they were on that day, it was the worst industrial accident in the history of the Lehigh Valley. At one time, we’ve never had 31 men killed in an accident and it wasn’t even at Bethlehem Steel.”

So what caused the blast? A press release the state Department of Labor & Industry issued April 10, 1942 said inspectors had discovered about 1,000 delayed action blasting caps that were expired were being used at Sandts Eddy.

According to the 1992 Morning Call story, Harry D. Immel, an inspector from Labor & Industry said unstable caps were being used and a premature explosion in hole No. 33 was caused by a rock falling on a cap. Immel criticized Hercules Powder experts: “They were guilty of one of the most flagrant violations of safety that I or any of the other investigators have ever heard of.”

Equipment used by quarry workers is on display at the Atlas Cement Museum in Northampton. (Evan Jones/The Morning Call)

Hercules answered by saying “if the company employee was responsible for the presence of the caps in question at this quarry, he was acting upon his own initiative and in direct violation of company practice.”

With the U.S. being forced to join World War II five months earlier, Grucela said the FBI was called in to see if there was sabotage.

“There was a thought at one time that it was espionage because it was during World War II,” Grucela said. “There was a theory that somebody had fired a rifle from across the (Delaware) river and ignited the dynamite, but that proved not to be true.”

The war raged for three more years after the incident, and afterwards people seemed ready to move on.

“The war ended, the men came home,” Grucela said. “I think the celebration of the end of the war, I think, kind of overlapped.”

The quarry closed in 1960 and the plant is now run by Ardent Mills, a flour-milling and ingredient company.

Memories of the disaster were kept alive, quietly, over the years. Grucela said he heard about it while growing up in the area and his daughter did a report on it while in elementary school. He credited Pany and his knowledge of the cement industry with keeping them alive and getting the memorial built before the 75th anniversary.

Pany said it’s important to commemorate the cement industry because cement from the Lehigh Valley was used to build the Panama Canal and the Empire State Building. At one time it had 30 cement companies with more than 60 plants.

“So you can imagine the thousands of cement workers that worked in these plants,” Pany said. “We still have four companies, they operate five plants, and they produce millions of tons because they’re much more automated.”

Werkheiser said worker safety is an issue that spans generations, which is why the Labor Council gathers annually for the Workers Memorial.

“That’s always been the whole reason for the memorial so that we more or less correct the problems of the past,” Werkheiser said.

Morning Call reporter Evan Jones can be reached at ejones@mcall.com.