It was one of the worst environmental disasters in modern history, and one of the biggest scandals. From 1932 to 1968, the Chisso chemical company released mercury- contaminated wastewater into the Minamata Bay in Japan, and tens of thousands of local residents, eating seafood from the bay, suffered from mercury poisoning.
Though the causes of “Minamata disease” were well understood by 1959, the company and the local government did little. The effects were obvious enough that local cats were said to have “dancing cat fever,” and children developed “pink’s disease,” in which their skin became pink and peeled. Other symptoms included weakness and loss of muscle control, numbness in the hands and feet, damage to vision, hearing and speech, and, in more severe cases, insanity, paralysis, coma, and death. Unborn children were especially at risk, with effects including brain damage, blindness, seizures, and the inability to speak.
At least 50,000 people were affected. 1,784 died and more than 10,000 received financial compensation from Chisso Corporation.
Out of this disaster came an international treaty known as the Minamata Convention on Mercury, which over 140 countries have signed. It regulates a range of products, processes and industries where mercury is used or emitted, and it will prohibit the manufacture of thousands of products that contain mercury by 2020, except where countries have requested an exemption for an initial five-year period. These products include batteries, compact fluorescent lamps, thermometers, soaps and cosmetics, among others.
Projection lamps have been granted an exemption because there is no good way to build a high-intensity lamp suitable for projection without mercury. Still, a number of projector manufacturers have introduced mercury-free light source technologies based on LED or laser. Casio, a strong supporter of the treaty, was one of the first to introduce mercury-free projectors back in 2010. Others have begun to follow suit. That said, there are hundreds of thousands of projectors using mercury vapor projection lamps still in our classrooms, conference rooms and homes, and so it’s helpful to understand the level of danger and some common-sense ways to deal with it.
Before we go much farther, we need to realize that there are various forms of mercury, and some are much more dangerous than others.
Among the most famous cases of mercury poisoning happened in 1997, when a researcher at Dartmouth College absorbed just one or two drops of dimethyl mercury into her skin through a latex glove. She suffered severe muscle and central nervous damage, from which she died after several months. Methylmercury, a related organic compound, is what caused the poisoning in Minamata.
Still, many older people remember playing with or even swallowing elemental mercury from a broken thermometer, with no apparent effects. They may believe that mercury is safe, but it’s just that liquid mercury is not absorbed easily by the skin or even the tissue of the digestive tract. Once in a landfill, however, it can be converted to methylmercury by bacteria and leach into groundwater in this deadly form.
Worse, elemental mercury evaporates, and inhaling the vapor is far more dangerous than ingesting the liquid.
The problem with mercury vapor is that the tissue in our lungs absorbs it readily, and from there it passes directly into the bloodstream and various body systems. While liquid mercury may not be very dangerous, it can be as it starts to evaporate in an enclosed space.
That danger is increased multifold if a projection lamp explodes or leaks as it fails. For the lamp to function, the mercury must be heated to several hundred degrees, and shouldof the day. it leak, it will spread rapidly through a room.
For that reason, you need to make sure that, if a bulb explodes, everyone knows to leave the room and knows where to report the problem. Next, you can start taking steps to contain, then eliminate the contamination.
But if a running projection bulb goes dark, it may or may not releasemercury vapor, and in most cases, people do not realize there is a danger.Most often a cracked bulb will not be discovered until a technician comesto replace it. This is a dangerous situation because people may stay in thatroom for the rest of the day.
How dangerous is this type of mercury release?
The Environmental Protection Agency has published a set of Acute Exposure Guideline Levels suggesting that if people are exposed to 0.33 mg of mercury vapor per cubic meter of air over an eight hour period, they have passed a threshold above which they could experience serious and irreversible health effects. At lower levels, most likely the effects would be non-disabling and reversible, but some individuals will experience serious, irreversible effects at lower levels not easily predicted.
The amount of mercury in a projection lamp will vary, but Philips states that their bulbs contain up to 23 mg of mercury; Ushio says 26 mg. A typical American elementary classroom will be 900 square feet, with a 10’ ceiling.That’s 9,000 cubic feet or 254.8 cubic meters. Release 26 mg of mercuryvapor into this space, we get a concentration of 0.10 mg/m³, about 1/3 the concentration the EPA warns can cause irreversible health effects for most people.
Release that same amount of mercury into a small conference room, home theater or family room, say 15’ x 20’ with an 8’ ceiling, that’s 26 mg into 34 cubic meters, for a concentration of .77 mg/m³. That’s more than double that same .33mg/m³ threshold.
Even at that high level, there’s no reason to panic. The time of exposure is as important as the concentration. At .77 mg/m³, the average adult could sit in that room for more than three hours without irreversible effects. And there is going to be some air change, so actually the time before damage will be longer. As long as people leave immediately, there’s no danger. Whether they leave is the crucial question.