It has recently come to the attention of the National Institute
for Occupational Safety and Health (NIOSH) that measurements of
the radioactive decay product "daughter" concentrations of radon
gas in a number of National Park Service caves are near the
occupational limits as set forth in Occupational Safety and Health
Administration's (OSHA) standards for uranium miners. National
Park Service caves in which one or more samples greater than 0.30;
working levels (WL) were found include Carlsbad Cavern National
Park, New Mexico; Lehman Caves National Monument, Nevada; Mammoth
Cave National Park, Kentucky; Oregon Caves National Monument,
Oregon; and Round Spring Cave in Ozark National Scenic Riverways,
Missouri. In addition to the radiation levels inside the caves,
buildings above the ground at Mammoth Cave, cooled with cave air,
had 0.6 WL alpha radiation. Studies of uranium miners have
shown that the alpha radiation emitted by the radon "daughters"
caused an increase in pulmonary malignancies which became evident
ten or more, years after individuals first started mining.
The OSHA requirements for uranium mines and deemed by Environmental
Protection Agency (EPA) applicable to natural caves are as follows:
0.1 to 0.2 WL -- monitor workspace at least once
yearly
0.2 to 0.3 WL -- monitor workspace quarterly
Above 0.3 WL -- monitor workspace weekly and maintain
exposure records on all exposed employees
1.0 to 2.0 WL -- immediate corrective action to lower
the concentration below 1.0 WL
Above 2.0 WL -- withdraw all workers not necessary to
lower the concentrations below 1.0 WL
Cumulative individual exposure shall not exceed 4
working level months in any calendar year
EPA states that the individual exposure limit of 4 WL months per
year recommended by OSHA cannot be characterized as safe since the
risk of lung cancer would be expected to double after 10 to 20
years employment. Therefore, it might be advisable to rotate
long-term employees working in high radiation areas.
NIOSH supports the above recommendations, and is taking this
opportunity to advise State Radiological Health officials of the
potential hazards for privately owned caves and "cave air" conditioned buildings.
Because there are a number of state and privately owned caves throughout the
United States, NIOSH would also recommend the radiation levels in these
caves be assessed.
Sincerely yours,
[signature]
Edward J. Baier
Deputy Director
Copies of this and other NIOSH documents are available from: