RBC Shield, LLC

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RADIATION EXPOSURE & PROTECTION FACTORS

OSHA Radiation Exposure Limits

The Occupational Safety & Health Administration (OSHA) has specified worker radiation exposure limits as 1,200 m/R (milli-roentgens) per quarter or 4,800 mR/year. For OSHA, these exposure limits are based on an 8-hour work day. However, based on a 24-hour day, this would permit an average of only .548 m/R exposure per day. But at an incident involving a "dirty bomb," the exposure would be much higher. So one has to determine how long one can stay in a shelter before that annual threshold is crossed.

However, once the threshold is crossed, it's impossible to say what the impact will be on the health of the person exposed. The age of the person, their general health, the strength of the continued radiation, the accumulated amount of exposure --- all are variables that must be taken into account.

The material below does not attempt to address these variables.

Instead, it only provides data that shows how RBC Shield® tiles can reduce the amount of radiation to which a person in a properly constructed shelter is exposed. The data is based on mathematical analysis of known variables that include the thickness of the lead, the strength of the radiation, and the distance of the shelter from the site of the incident involving a radioactive substance.

Examples of the Effect of Lead Thickness on Radiation Exposure

1. If exposure is to 2 oz. of Cesium-137 at 1/4 of a mile away, then varying levels of protection would result in the following m/R per hour exposure:

Zero protection: 8.35 mR/hour
1/8-inch lead: 5.54 mR/hour
1/4-inch lead: 4.05 mR/hour
1/2-inch lead: 2.34 mR/hour

One-quarter of an inch of shielding would allow a person to safely shelter-in-place for the following periods of time without exceeding OSHA's annual radiation exposure standards:

Approx.
Time
Accumulated Exposure
15 days
1,415 milli-roentgens
30 days
2,916 milli-roentgens
45 days
4,374 milli-roentgens

2. For exposure to the 1 oz. Cobalt-60 at the same distance, then the protection of varying levels of lead would be as follows:

Zero protection: 208.81 mR/hour
1/8-inch lead: 169.42 mR/hour
1/4-inch lead: 137.47 mR/hour
1/2-inch lead: 100.50 mR/hour

One-quarter of an inch of shielding would allow a person to safely shelter-in-place for the following periods of time without exceeding OSHA's annual radiation exposure standards:

Approx.
Time
Accumulated Exposure
12 hours
1,644 milli-roentgens
16 hours
2,466 milli-roentgens
24 hours
4,795 milli-roentgens
35 hours
4,795 milli-roentgens