Information Notice No. 85-87: Hazards of Inerting Atmospheres
SSINS No.: 6835
IN 85-87
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
November 18, 1985
Information Notice No. 85-87: HAZARDS OF INERTING ATMOSPHERES
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP) and fuel facilities.
Purpose:
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.
Discussion:
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.
8511150098
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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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IN 85-87
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
Attachments:
1. Event Summaries
2. List of Recently Issued IE Information Notices
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Attachment 1
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November 18, 1985
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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
incident.
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.
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Attachment 1
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2. Although the equipment was available, oxygen air sampling was not
performed.
3. "Buddy system" for the first entry into a confined space was not
employed.
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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