Nothing is finer in life than sitting in your recliner, watching sports on TV and eating fried, lard encrusted food. Surprisingly, it turns out that it may have some serious health consequences. No, I’m not talking about the obesity epidemic. I’m talking about radioactive La-Z-Boys. In 1998, an Indiana company unknowingly used metal contaminated with the radioactive isotope Cobalt-60 to make brackets for 1,000 La-Z-Boy Reclina-Rockers. Fortunately, the problem was discovered when metal leftovers were sent to a scrap yard that detected the radiation and refused the shipment. The discovery led to a massive state and federal effort that managed to recall all of the recliners before they had left the warehouse.
A spokesman for the No-Sag Products Co. that manufactured the brackets stated that any health threat was minimal, but asked the federal government to create standards for the radioactive material content of consumer products. While there may not be standards for radioactive content, there are standards for the radioactive dose allowed to be given to members of the general public. In radiation therapy, we have to design our facilities to meet those standards. Would a radioactive La-Z-Boy meet those standards? Was the health threat only minimal?
In the United States, the allowable dose that a member of the general public can receive is 0.02 mSv in a week (radiation workers are allowed to receive a higher dose). Internationally, the allowable limit for the general population is lower, only 0.004 mSv in a week. A mSv is a milli-Sievert, a unit of radiation equivalent dose. One Sievert is equal to 100 rem, a radiation dose unit that may be more familiar. This level is set by NRC based on the study of the health effects of radiation by organizations such as the National and the International Council on Radiation Protection. As a comparison, the background radiation that the average person receives from the environment is around 0.05 mSv in a week.
The article states that the radiation emitted from the metal brackets was 0.02 millirems or 0.0002 mSv per hour. It’s not stated at what distance this is measured. Distance is important because the dose from radiation decreases as the square of the distance from the source. So halving the distance from the source would increase the dose by four times. For the purposes of this calculation, we will assume that it was measured at the distance a person in a recliner would be from the metal bracket. The total dose in a week would therefore be 0.0336 mSv. This is greater than the allowable limit.
However, a person would (hopefully) not spend an entire week sitting in a recliner. So we can decrease the total dose by the proportion of time it would be occupied by a person. This is called the occupancy factor. In radiation shielding design, this factor is used to take into account the fact that certain areas, such as waiting rooms, will not be occupied by people 100% of the time. Therefore, the allowable dose rate can be increased. The NCRP recommends that areas such as offices or nurses stations would have an occupancy factor of 1. This reflects the fact that people might occupy those areas for an entire workday. Areas that may be empty some of the time such as parking lots or elevators with operators would have an occupancy factor of 1/4. Areas like waiting rooms or toilets would have an occupancy factor of 1/16.
If we assume that a person spends four hours a day in a recliner, they would receive a dose equivalent of 0.0056 mSv in one week. This would be below the limit in the US, but above the international limit. This also assumes that the measured dose rate of 0.0002 mSv per hour is at the position the person would be sitting. So, in fact, the actual dose rate could be higher. Also, if a person spends more time in the recliner, their dose rate would increase. Still, this analysis bears out the statement that the health threat was probably minimal.
The important thing to keep in mind is that these limits are intended to protect the public from the unfortunate, but unavoidable, side effects of using radiation to diagnose and treat disease. They are not meant to allow the sale of radioactively contaminated consumer goods. The science behind the risk from low levels of radiation is still unsettled, but there should be no question that if radioactive exposures can be prevented, that they should be. This is the principle in radiation safety known as ALARA, or As Low As Reasonably Achievable. It seems to me that it is reasonable to require that a recliner be free from radioactive contamination. The actual medical risk in this case might have been low, but why allow any risk at all?
