Information Notice No. 85-87: Hazards of Inerting Atmospheres

                                                         SSINS No.: 6835 
                                                            IN 85-87       

                                UNITED STATES
                           WASHINGTON, D.C. 20555

                              November 18, 1985

Information Notice No. 85-87:   HAZARDS OF INERTING ATMOSPHERES 


All nuclear power reactor facilities holding an operating license (OL) or a 
construction permit (CP) and fuel facilities. 


This information notice is provided to alert licensees to events that have 
occurred at nuclear power plants where personnel were exposed to 
oxygen-deficient atmospheres immediately dangerous to life or health (IDLH).
This notice focuses on personnel safety issues that are largely outside the 
scope of NRC's nuclear safety requirements. However, the information should 
be helpful to licensees in their efforts to maintain safe working conditions
for their employees. 

It is expected that recipients will review this information for 
applicability to their facilities and consider actions, if appropriate, to 
preclude similar problems at their facilities. However, suggestions 
contained in this notice do not constitute NRC requirements; therefore, no 
specific action or written response is required. 

Description of Circumstances: 

A brief description of the events is provided in Attachment 1. In each 
event, workers were physically affected and required prompt medical 
attention. The severity of physical effects of inert-gas exposure ranged 
from disturbed respiration to loss of consciousness. In one event, two 
deaths resulted from exposure in an IDLH area. 


While not toxic themselves, inert gases such as nitrogen, argon, and carbon 
dioxide can displace normal air and thereby create oxygen-deficient IDLH 
areas. Argon and carbon dioxide have specific gravities relative to air of 
1.5 and 1.4, respectively, and thus can present hazards even in open-topped 
areas. Even after good faith efforts to purge and ventilate areas known to 
be inerted, a "de-inerted" area can present personnel hazards. Pockets of 
inerting gas can linger in low-lying areas of the affected spaces. In areas 
where oxygen is in the 8-12% range, unconsciousness can occur rapidly and 
without warning. 


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Unprotected exposure to an atmosphere containing less than 6% oxygen by 
volume (at sea level) causes incapacitation after only, a few breaths, 
convulsive movements, and death in a few minutes. 

Title 29, Code of Federal Regulations, Part 1910.134, provides certain 
regulatory requirements for worker protection against respiratory hazards. 
These Occupational Safety and Health Administration (OSHA) regulations 
include (among other things) requirements for "appropriate surveillance of 
work area conditions," written procedures for the proper use of respirators 
in dangerous areas, and special provisions for communication and rescue from
hazardous working areas. However, in three of the four events discussed, 
unprotected workers unknowingly entered existing oxygen-deficient IDLH 
areas. In all but the Hope Creek event, an effective workplace surveillance 
program (including periodic air quality sampling and hazard area 
controls/posting) could have identified hazardous areas and possibly 
prevented worker entry into IDLH areas. Along with the workplace 
surveillance program for hazards identification, procedures establishing 
entry and work requirements can form the basis of an effective 
non-radiological hazards control program. 

Several information documents are available that could be useful to 
licensees trying to improve their worker safety programs. NUREG/CR-3551, 
"Safety Implications Associated with In-Plant Pressurized Gas Storage and 
Distribution Systems in Nuclear Power Plants" (May 1985), provides a 
detailed, thorough technical review and offers a broad perspective for many 
aspects of using compressed gases. The NUREG discusses many elements 
important to plant safety that relate directly to a non-radiological hazards
control program and, personnel respiratory protection, including (1) 
physical properties and hazards of gases, (2) failure modes of gas systems, 
(3) incidents, and (4) potential hazards. Information Notice No. 81-26, Part 
4, "Personnel Entry Into Inerted Containment" (August 1981), is another 
useful reference which discusses a non-emergency entry into a fully inerted 
BWR containment at power. The notice discusses the entry hazards, provides 
guidance, and lists other pertinent references. The Institute for Nuclear 
Power Operations' Good Practice "Safe Work Procedure for Enclosed Volumes" 
(OA-101, Rev. October 1983) provides procedural guidance for safely entering
and working in potentially IDLH confined spaces. Other related 
correspondence includes: IE Circular 80-03, "Protection From Toxic Gases" 
(March 1980), and Information Notice No. 83-62, "Failure of Redundant Toxic 
Gas Detectors Positioned at Control Room Ventilation Air Intakes" (September 
1983). These two issuances focus primarily on maintaining adequate 
protection of control rooms against toxic gas threats. 

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                                                         November 18, 1985 
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No specific action or written response is required by this information 
notice. If you have any questions about this matter, please contact the 
Regional Administrator of the appropriate regional office or this office. 

                                   Edward L. Jordan Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  James E. Wigginton, IE
                    (301) 492-4967

                    Roger L. Pedersen, IE
                    (301) 492-94

1.   Event Summaries
2.   List of Recently Issued IE Information Notices

                                                         Attachment 1     
                                                         IN 85-87         
                                                         November 18, 1985 
                                                         Page 1 of 2      

                               Event Summaries

Hope Creek                                        Event Date: September 1985

An inadvertent initiation of the carbon dioxide fire suppression system 
(FSS) caused the release of approximately 10 tons of cardox (liquid carbon 
dioxide under pressure) into one of the four diesel generator fuel oil 
storage tank rooms. The affected room pressurized and carbon dioxide leaked 
into adjacent areas where several workers were overcome. Twenty-three people 
were transported to nearby hospitals with one individual listed in serious 
condition upon arrival (condition later improved to "guarded"). The plant 
was evacuated, and search and rescue teams reported some difficulty in 
accounting for all construction personnel during the search to ensure all 
persons had been evacuated. 

The cause of the 10 ton continuous discharge (system designed for 2-ton 
"burst" release of C02) is still under review, but believed to be caused by 
a fault in the FSS control system initiated by moisture electrically 
shorting FFS control circuitry. The licensee and OSHA are investigating the 

Rancho Seco                                       Event Date: August 1985 

With the plant in a cold, shutdown condition, a nitrogen inerting blanket 
was placed on a moisture separator reheater. The nitrogen leaked past 
several shut valves into the main condenser. A non-licensed operator, while 
walking down the condensate system, stopped near the open condenser manway. 
The operator passed out because of an apparent local IDLH area created by 
nitrogen escaping the condenser. Prompt and effective rescue/first aid was 
provided by an accompanying assistant, and the operator was transported to 
the hospital. No permanent injury resulted from the incident. As a result of
a licensee review of the lessons learned from the event, the licensee has 
improved its hazards controls program for using inerting gases by increasing
atmosphere sampling, providing appropriate hazard postings to alert workers,
and analyzing the potential effect on associated systems (e.g., potential 
leak paths). 

D.C. Cook Nuclear Plant                           Event Date: September 1976

Two workers were killed in a recirculation pit (sump) by asphyxiation from 
argon inerting gas used to support welding on stainless steel piping. After 
the welding was completed, the argon purge was not secured and gas leakage 
from the faulty argon purge-pipe connection filled the pit. When a workman 
entered the pit to remove the purge connection, he was overcome by the 
inerted atmosphere. He and one of two fellow workers attempting rescue were 
killed. A licensee safety review of the incident revealed several work 
practice deficiencies including: 

1.   Local ventilation for the pit was available, but not used before entry.

                                                         Attachment 1     
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                                                         Page 2 of 2      

2.   Although the equipment was available, oxygen air sampling was not 

3.   "Buddy system" for the first entry into a confined space was not 

Other Events 

Other instances of problems have occurred during the past few years, many of
which are not reported formally to the NRC. In a typical example, a health 
physics (HP) technician was overcome by an oxygen deficient atmosphere in a 
steam generator (SG). The secondary-side of SGs are often nitrogen inerted 
to minimize oxygen uptake during non-operational modes. In this case, the 
wrong SG was purged of its inerting atmosphere, and an HP technician (when 
entering the still-inerted SG) was overcome. Another HP technician on the 
scene promptly pulled the asphyxiated technician from the IDLH area. No 
lasting injuries from the event were noted. 

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