On July 24, 2020, at 1:20 p.m., an accidental release of approximately 100 milliliters of silicon tetrachloride seriously injured two contract workers. At the time of the event, contract workers were disassembling a 2-inch flange to remove a blind (a solid metal plate used to isolate equipment) before reinstalling a section of piping that had been removed and cleaned. This type of equipment opening is commonly called a “line opening” or “performing a line break.”
The contract workers performing the line opening wore personal protective equipment (“PPE”), including full-face respirators, chemical gloves, and fall protection. The contractor’s pre-job safety analysis form did not require the use of chemical suits or rubber boots because the piping system had been disassembled the previous day for the cleaning activity. This additional protective equipment was required under the facility’s safe work permit, which authorized the contractor to perform the line-opening work. As the workers disconnected the flanged connection bolts, they were splashed with corrosive liquid silicon tetrachloride that had leaked past an isolation valve and pressurized the piping, seriously injuring the two contract workers with chemical burns.
OSHA investigated the event and cited the contractor for failing to ensure workers used the chemical suits and rubber boots required by the safe work permit. OSHA’s investigation file noted confusion between the contractor and the facility about line-opening work and who could perform it. The contractor told OSHA that the company had performed many similar equipment opening tasks at the facility. The facility personnel, however, told OSHA that only facility employees were allowed to perform this type of line-opening work.
The scope of the facility investigation was narrow and insufficient. The investigation found that the contractor was responsible for the incident because the contractor (1) had performed this line opening work and (2) did not use suitable PPE during that work—violations of the facility’s policies and administrative controls. However, the facility’s investigation did not evaluate its role in the incident’s causation.
For example, facility personnel authorized these contractors to perform the line opening work, which the facility stated its policies require its employees to perform. In addition, the facility did not ensure that this piping was effectively isolated, flushed, and drained to remove silicon tetrachloride before tasking contract workers with performing the line-opening work.
Furthermore, the facility’s policies required a facility manager to confirm that personnel performing line-opening work had the required PPE, but this did not occur.
Probable Cause
Based on the factual investigative information the CSB obtained from the facility and OSHA, the CSB determined that the probable cause of the accidental silicon tetrachloride release was the facility’s failure to effectively isolate, flush, and drain the piping system before turning it over to the contract workers for disassembly. Not using PPE that could have protected workers from splashes of corrosive silicon tetrachloride contributed to the severity of the incident.
Source: https://www.csb.gov/assets/1/6/csb_incident_reports_volume_one_2025-01-14_rev_1.pdf