idleprocess said:
I think the paranoia about hazardous substances is blown out of proportion. Eliminating lead, mercury, heavy metals and the like from use in applications where they might come into routine contact with people or the environment is a good thing. Leaded gasoline, lead water pipes, mercury cells, paint, etc etc etc - they all came into daily contact with people and/or were eventually dumped into the environment... But totally eradicating mercury, lead, etc from electronics? What's the point? I can see mandating the safe disposal of such things, but given the small quantities and their typical isolation from day-to-day contact with humans and the environment... why? I think this paranoia deserves as much scorn as the mass hysteria over cell phones and their statisticly non-existent association with brain cancer.
I have a metallic filling from the early/mid-80s. I imagine it has some trace quantities of mercury. My only concern is that it will fall out someday. I'm sure that there are plenty of other factors that could explain any dulling of my intellect...
The problem with lead in electronics isn't so much the electronics or when they end up in a land fill, but the fumes produced by the wave solder systems, and repair work. This is why many radiator repair shops have been closed. People who work in those envirornments often have substantially elevated lead levels in their blood.
The lead vapor from these activities went directly into the atmosphere. The virtual elimination of lead tetraethyl form gasoline has resulted in a marked reduction in lead levels in human blood.
Sodium Vapor lamps (HPS) also rely on small amounts of mercury to light them. At room temperature, the vapor pressure of sodium is so low, that ignition is virtually impossible, so these lamps light initially as mercury vapor (which has a much higher vapor pressure than sodium at room temperature), and as the mercury vapor heats up the arc tube the balance of the mercury vaporizes, and the resulting heat from the discharger causes the sodium to start to vaporize, as it vaporizes, it heats and still more sodium is vaporized, the process continues until almost all of the sodium in the tube is vaporized, at which point the lamp is fully lit, and the portion of output that is mercury vapor has been reduced to insignificance.
The other posters are correct, the big hazard in most HID's come from large installation, and the fact than an envelope can shatter, and the lamp not fail (there are lamps made that are guaranteed to fail if the envelope failes). The result can be enormous UV output, but because of the setting, in places such as a high school gymnasium, with all the lights, that no one notices that the envelope on one or more lamps out of dozens has failed, and people start showing up with sunburn, burned cornea's, and other indications of extreme UV exposure.
