https://chroniclingamerica.loc.gov/lccn/sn87057262/1918-05-20/ed-1/seq-1/#date1=1918&index=9&rows=20&words=HUNDRED+MISSING+TWO&searchType=basic&sequence=0&state=&date2=1918&proxtext=two+hundred+missing&y=0&x=0&dateFilterType=yearRange&page=1

Two hundred workers are missing in an industrial plant explosion at the Aetna Chemical plant in Oakdale, PA. Worker cabins near the plant were destroyed by TNT. Twenty-five bodies were found in one small area of the plant. 

Source: "Two Hundred Employees Missing," The Daily Gate and Constitution-Democrat, Keokuk, Iowa, May 20, 1918. Page 1, Column 5.