Investigation Report RE: Nitrogen Asphyxiation at Union Carbide Plant in Hahnville, Louisiana


		AcuSafe -> August 2000 Newsletter
		Investigation Report RE: Nitrogen Asphyxiation at Union Carbide Plant in Hahnville, Louisiana

This article is based upon a Chemical Safety Board investigation report dated February 23, 1999, and represents the findings of fact and conclusions of this document.

On March 27, 1998, at approximately 12:15 pm, two workers at Union Carbide Corporation's Taft/Star Manufacturing Plant (the plant) in Hahnville, Louisiana, were overcome by nitrogen gas while performing a black light inspection at an open end of a 48-inch-wide horizontal pipe.

The 48-inch pipe was open because chemical-processing equipment had been shut down and opened for major maintenance. Nitrogen was being injected into the process equipment primarily to protect new catalyst in reactors from exposure to moisture. The nitrogen was also flowing through some of the piping systems connected to the reactors. The nitrogen was venting from one side of the open pipe where it had formerly been connected to an oxygen feed mixer. No warning sign was posted on the pipe opening identifying it as a confined space or warning that the pipe contained potentially hazardous nitrogen.

The two workers had placed a sheet of black plastic over the end of the pipe to provide shade to make it easier to conduct the black light test during daylight. While working just outside the pipe opening and inside of the black plastic sheet, the two workers were overcome by nitrogen. One worker died from asphyxiation. The other worker survived but was severely injured. The following picture depicts the area where the accident occurred.

Based on these facts, the Chemical Safety Board identified two root causes and one contributing cause to the event.

Root Causes:

1. Procedures to control potential hazards created by erecting temporary enclosures around nitrogen-containing equipment were inadequate.
The plant did not have adequate procedures in place to address potential hazards created by the use of temporary enclosures. Temporary enclosures erected around tanks, vessels, pipes, or similar equipment that contain hazardous material may trap a dangerous atmosphere if the equipment leaks or vents substances, such as nitrogen, into the enclosure.

2. Nitrogen and confined space hazard warnings were inadequate.
Personnel were not aware of the hazard of the nitrogen flowing out of the open pipe that they were working on, even though one of injured individuals had earlier directed that nitrogen be injected into the equipment. No warning signs were posted identifying the pipe as a confined space or alerting personnel to the presence of nitrogen.

Contributing Cause

Personnel were unable to detect hazardous levels of nitrogen because this gas cannot be detected by human senses. Odorization of nitrogen could have warned personnel that a hazardous atmosphere was present and thereby prevented the incident.

Recommendations were primarily directed at Union Carbide to provide warning signs alerting workers to the confined space danger, and of the specific nitrogen hazards present. They also recommended that Union Carbide ensure that the plant safety program addresses the control of hazards created by erecting temporary enclosures around equipment that may trap a dangerous atmosphere in the enclosure if the equipment leaks or vents hazardous material. One other recommendation directed at NIOSH suggested that a study be conducted concerning the appropriateness and feasibility of odorizing nitrogen in order to warn personnel of the presence of nitrogen when it is used in confined spaces.