United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 91-37: Compressed Gas Cylinder Missile Hazards

                              UNITED STATES 
                      NUCLEAR REGULATORY COMMISSION 
                   OFFICE OF NUCLEAR REACTOR REGULATION 
                         WASHINGTON, D.C.  20555 

                              June 10, 1991 


Information Notice No. 91-37:  COMPRESSED GAS CYLINDER MISSILE HAZARDS 


Addressees: 

All holders of operating licenses or construction permits for nuclear power 
reactors. 

Purpose: 

This information notice is intended to alert addressees to an event 
involving Halon surveillance testing which resulted in an uncontrolled 
acceleration of the Halon gas cylinder.  It is expected that recipients 
will review this information for applicability to their facilities and 
consider actions, as appropriate, to avoid similar problems.  However, 
suggestions contained in this information notice do not constitute NRC 
requirements; therefore, no specific action or written response is 
required.

Description of Circumstances: 

On February 26, 1991, biannual surveillance testing of the services 
building Halon fire suppression system was being performed at the River 
Bend Station (RBS) in order to verify the Halon content of each of the fire 
suppression system cylinders.  The H-250 cylinders, which are nominally 3 
feet long and 16 inches in diameter, are pressurized to 350 psig with 190 
pounds of Halon and weigh about 350 pounds when fully charged.

The technicians performing the surveillance disconnected a Halon cylinder 
from the fire suppression system, removed the cylinder from its rack, and 
transported the cylinder to the service building restroom/shower area for 
weighing.  At the weighing station, the technicians removed peripheral 
fittings from the Halon cylinder as required by the surveillance procedure 
so an accurate weight measurement of the cylinder and its contents could be 
obtained.  While removing these fittings, a technician incorrectly removed 
one fitting which vented the cylinder valve and caused the cylinder valve 
to open.  The contents of the Halon cylinder rapidly discharged to the 
atmosphere, causing the Halon cylinder to become an uncontrolled 
projectile.  

Two technicians were injured, one seriously, as a result of this mishap and 
extensive damage was caused in the shower and restroom area where the work 
was being done.  For example, gouges were made in the tile of a shower 
wall, ceramic tile was knocked off a concrete floor leaving a two inch deep 
gouge in the concrete, tiles were knocked off a suspended ceiling, and a 
hole (approximately one foot square) was made in a six-inch cinder block 
wall.


9106040346 
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The licensee reviewed the circumstances surrounding this event and 
determined that the surveillance was not properly conducted.  First, after 
the cylinder had been disconnected from the fire suppression system, the 
technicians failed to install the anti-recoil plug in the cylinder valve 
outlet port.  Installation of this anti-recoil plug would have prevented 
the rapid release of Halon that occurred.  Second, the fitting that was 
removed which vented the cylinder valve and caused the cylinder valve to 
open was a Schraeder valve, which should have been left installed.  The 
surveillance procedure was not very detailed, however, and reliance was 
placed on the qualifications and training of the individuals performing the 
surveillance.

Discussion: 

The event that occurred at RBS fortunately did not result in any damage to 
safety-related equipment.  However, compressed gas cylinders are typically 
located throughout the plant in both safety-related and nonsafety-related 
areas, and different circumstances could easily have resulted in extensive 
damage to safety-related equipment.  For example, the control room cabinets 
at RBS contain small spherical Halon cylinders which are subjected to the 
same biannual surveillance testing as the services building Halon cylinders 
previously described.  The spherical Halon cylinders are pressurized to 360 
psig with 25 pounds of Halon and weigh about 50 pounds when fully charged. 
An uncontrolled acceleration of one of these cylinders in the control room 
could cause serious injury to control room personnel and significant damage 
to safety-related equipment located in the control room.  

NUREG/CR-3551, "Safety Implications Associated with In-Plant Pressurized 
Gas Storage and Distribution Systems in Nuclear Power Plants," May 1985 
provides additional information related to this topic and cautions that 
portable compressed gas cylinders can pose a significant missile hazard if 
not properly controlled.  Portable compressed gas cylinders are used 
throughout nuclear power plants to provide, for example, fire suppression 
agents, breathing air, nitrogen and hydrogen for instrument calibration and 
surveillance testing purposes, and gases for various welding applications.

Factors that contributed to the event that occurred at RBS include 
inadequate procedures and inadequate training and qualification of the 
technicians performing the surveillance.  The licensee provided additional 
training to individuals who perform maintenance and surveillance on 
compressed gas cylinders, and additional details were included in the 
maintenance and surveillance procedures to avoid future mishaps of this 
nature. 
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                                                          IN 91-37
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This information notice requires no specific action or written response.  
If you have any questions about the information in this notice, please 
contact one of the technical contacts listed below or the appropriate NRR 
project manager. 




                                 Charles E. Rossi, Director Division of 
                                 Operational Events Assessment Office of 
                                 Nuclear Reactor Regulation


Technical Contacts:  Phillip H. Harrell, RIV
                     (817) 860-8250

                     James E. Tatum, NRR
                     (301) 492-0805


Attachment:  List of Recently Issued NRC Information Notices
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