Sarnicki says employees sheltered in place because there was a release of a 15 percent solution of ethyl aluminum dichloride.

Xofigo, also called Radium-223 dichloride, is designed to target bone metastases from prostate cancer that cannot be treated by standard hormone therapy.

Bayer said last year that Radium-223 dichloride could become a "blockbuster" product with annual sales of least 1 billion euros.