OBT Oils cont'd

DOE-HDBK-1184-2004

on liquid tritiated oil (Trivedi, 1995) indicates that the 80:10:10 assumption should

be conservative.

The latter two of the three expected OBT oil components can in fact diffuse through

the skin. The HTO component can migrate quickly through the skin into body water

and intake should be assessed via urine bioassay. Small molecule OBT can also

migrate through skin and is considered soluble; intake of this component should

also be assessed via urine bioassay. Estimation of potential absorption intakes of

HTO and soluble OBT resulting from direct skin contact with liquid oil should be

performed via analysis of oil samples for total tritium, and application of the above

80:10:10 ratio. Inhalation intakes of vapors liberated from volatile HTO and soluble

OBT components of oil can also occur. Estimation of potential vapor intakes should

be performed via monitoring of air above the oil by ion chamber.

Large molecule OBT is considered to be insoluble. Estimates of diffusivity of large

organic molecules such as pump oils in polymer films, extrapolated from data for

chemically similar but smaller molecules (Rogers, 1985), suggest that oils migrate

extremely slowly (if at all) into and though polymeric materials. For this reason, the

large molecule OBT component of oils is estimated not to absorb into (or through)

skin and therefore not to impart skin (or other tissue) dose via this pathway.

The large molecule component of oil is not volatile. However, this oil component

can be dispersed into air from the either operation of equipment or the sudden

release of residual pressure, and therefore can be inhaled as a mist (and deliver a

lung dose). Tritium from the insoluble large oil molecules does not dissolve into the

body, due to the stability of the carbon-tritium bond in oils. Oil absorption in lung

tissues is low, and clearance rate of oil from lung could be as slow as that of

particulates. Therefore, an oil mist intake should be treated like an intake of solid

particulate OBT (i.e., as an intake of ITP). Oil mist inhalation should be monitored

by air sampling and assessed as ITP inhalation.

Estimation of potential inhalation intakes of OBT oil mists should be performed via

analysis of oil samples for total tritium, and application of the above 80:10:10 ratio.

Because OBT oils are expected to be a mixture of HTO, soluble OBT, and insoluble

OBT as discussed above, radiological protection planning for activities involving

OBT oils s hould consider potential intakes of, and air monitoring for, all three

components. To avoid mist formation, energetic activities involving unencapsulated

OBT oil should be discouraged.