NSLS ESH Highlight #15

Overheating Beamline Component Creates Smoke

Date: March 31, 1999 (Rev. 5/18/99)
Editor: NSLS ESH Staff

At 01:30 hrs. on March 22, an experimenter prepared to leave his beamline. Part of his setup involved directing heated (200° C) nitrogen gas onto a sample. He checked the temperature apparatus (Omega controller, heater and gas line with a thermocouple at the opening adjacent to the sample), the nitrogen supply (a new cylinder was in use; the experimenter estimated that the cylinder should last for 2 days) and the gas flow (detected with a finger on top of the hot N2 gas line). For the purposes of the experiment, the sample had to remain at 200° C. Satisfied that all was in good order, the experimenter went home.

At 07:20 hrs, an Operations Coordinator in the vicinity of the beamline smelled smoke. He located the hutch, opened it, noted that the nitrogen gas tube heating jacket was blackened and smoking (no fire). He removed power from the apparatus and tagged out the beamline. Then, with the help of Security, he contacted the experimenter in the on-site dorms and also reported the incident to the Fire Captain (the smoke had been insufficient at that time to set off a fire alarm).

LESSONS LEARNED

Upon examination of the experimental apparatus and from discussions with the experimenter, it appears that the N2 cylinder ran out of gas. When the gas flow stopped, the thermocouple cooled down. This resulted in a call for more current to the heater. The heating jacket increased in temperature and overheated to a black color giving off the smoke that was detected by the OpCo. Experimenters need to be alert to equipment designs that allow simple failures to cause safety problems or equipment damage. The following additions to the experiment would have avoided this incident.

• The apparatus should have an adequate high temperature electrical power shut off with a sensor at the heater rather than being located at the gas discharge.
• Nationally recognized testing laboratory (UL, etc.) components should be used when possible. Where custom made equipment is used, then applicable standards (ANSI, IEEE, etc.) must be followed. The equipment must be listed as part of the Experimental Safety Approval Form.
• The N2 gas system should have proper pressure gauging, a flow volume and direction sensor as well as the capability of removing electrical power to the apparatus should gas flow cease.
• Use of house air would be an improvement; a cylinder contains a finite amount of gas.
• Spokespersons and Local Contacts should maintain oversight to minimize experimental hazards at their beamlines.

The NSLS provides a variety of support services to the Users.

Contact: John Gallagher (x5770, pager 0875) for experimental electronics support.