23 April 2009

Break a CFL? Don't panic.

Lisa Sharkey had a piece in yesterday's Huffington Post where she described her panic over a broken compact fluorescent light bulb in her home. She then listed a series of clean up procedures that could only have been written by a personal injury attorney. Sheesh. Calm down already!

All fluorescent light bulbs contain elemental mercury. That includes the long, skinny ones in offices and schools. Elemental mercury is a naturally-occurring heavy metal that's also a neurotoxin in high enough doses. Elemental mercury is a liquid at room temperature and it evaporates into a gas easily. That gas glows when electricity passes through it. Hence its use in light bulbs. Mercury has a long list of practical uses and is found in everything from Mercurochrome to mascara. High concentrations of elemental mercury are more damaging as a gas than as a solid, so there are some sensible precautions you'll want to take should you break one of these bulbs.

But let's get a little perspective first and do some math.

Let's say you break a CFL containing five milligrams of mercury in your child’s bedroom. Further, let's say that bedroom has a volume of 25 cubic meters (that's a medium-sized bedroom). For the sake of illustration, let's assume that the entire five milligrams of mercury in the bulb vaporizes immediately. This would result in an airborn concentration of 0.2 milligrams per cubic meter. This concentration will decrease with time, as air in the room leaves and is replaced by air from outside or from a different room. So even if you do nothing, the concentrations of mercury in the room will likely approach zero after about an hour or so.

Under these relatively conservative assumptions, this level and duration of mercury exposure is not dangerous, since it's lower than the US Occupational Safety and Health Administration (OSHA) standard of 0.05 milligrams per cubic meter of metallic mercury vapor averaged over eight hours. 

To equate the level of exposure in our broken bulb scenario with OSHA's eight-hour standard Imagine the immediate level of mercury in the room immediately after the bulb broke to be 0.2 milligrams of mercury per cubic meter. If we assume the air in the room changes every hour, then the eight-hour average concentration would be .025 milligrams per cubic meter.

See? No need to panic. While I wouldn't call it harmless exactly, it's not something you need to call a Hazmat team over.

So, in the event that you break a CFL, open a window to speed up the dispersal of the mercury vapor. If it makes you feel better, leave the room for a half an hour. Then come back and clean up the broken glass. 


  1. Great Post! I remember breaking a thermometer as a child and having my mother scream at me not to touch the mercury.

    There are greater amounts of mercury found in old thermostats. Unfortunately, we don't hear much on how to dispose of them properly.

  2. Thanks!The mercury in CFLs seems to be the chicken little cause du jour. I'm not discounting the toxicity of mercury for a second, it's just that people need to calm down already. Toxicity is a matter of how much you're exposed to. If you want to worry about something, worry about the strontium released when coal's burned, it's far more dangerous a substance.

  3. People probably eat more mercury in fish than they'd ever get from a broken lightbulb. All the fish I've eaten in my lifetime, I'm surprised I'm not running around saying things like "Twinkle, twinkle, little bat! How I wonder what you're at."

  4. Hurray! An actual scientist weighs in.

  5. Paul, don't know what I dislike more. The CFL lightbulbs or the Politicians that are promoting them. In our Province they actually gave out free CFL's bulbs to every household and spent billions of $$$$$ on Energy Advertising campaigns.....both with TAXPAYERS money. Frankly, educating people to turn off their 'damn' lights when they left a room, wud have been just as effective AND cheaper!!!

  6. I changed out my incandescent bulbs for CFLs about a year ago and my electric bill really did drop noticeably. The bulbs I use have a yellow cast to them, so they don't feel or look like fluorescent light. I favor their use pretty strongly. With that said, I'd love to know how much money Phillips and GE are spending on political lobbying to enact this switch world wide. Hmmm.

  7. Paul, re 'political lobbying' and the 'monies'. You can be sure we will never know.

  8. I am Lisa Sharkey who wrote the blog post about CFLs about which you refer in this article. I am not the person who wrote the guidelines, those are the actual US Federal Government's official instructions about what to do when a CFL breaks in your home. I think that someone in the government needs to clarify the danger if there is any and improve warning labels, or if there is nothing to worry about at all, then they should modify their instructions for cleanup as such.
    If you want to see some great green designs go to www.dreaminggreenbook.com

  9. Hey Lisa, thanks for your comment. I realize that the guidelines you listed weren't yours and I still maintain that they could only have been written by a personal injury attorney. Clearly, those guidelines are written to avoid a lawsuit and the're intended for a scientifically illiterate populace. Sadly, this includes most people. Regardless what the "official policies" are, a familiarity with chemistry is all it takes to understand that the mercury in a CFL poses little threat. The glass that encloses those 4mg of mercury pose a far greater danger.

    I cannot understand why someone who's spooked by the mercury content in a CFL would bring them into her home in the first place. CFLs aren't dangerous. They are a terrific way to use less electricity though.

    Thanks for your piece in the Huffpo by the way. You gave me a topic I wouln't have covered otherwise. Oh wait a minute, I got an e-mail last week from a woman who's afraid that CFLs emit harmful gasses. I doubt I could have kept my cool had I used that as a stepping off point to talk about the safety of CFLs.

  10. I have read some research done by Stanford university indicating that the levels of mercury vapor rose and fell over a two month peiod after having broken the bulb. this was after the researchers cleaned up the broken CFL according to EPA guidlines, and the research indicates that whenever the spot where the CFL broke is "agitated" by someone walking over it or vaccuming the area the vapors are released. the amount of vapors are high at the child level of about one foot, when agitated, this leads me to feel unsafe ever letting a child crawl across a floor that has evr had a CFL broken on it. Anyone can look up the research if they so wish.

  11. What are you considering a "high" level of mercury vapor? As a naturally-occurring element, mercury is impossible to avoid. As is lead, arsenic and any other toxic substance you can name. The key to toxicity is dose, not the existence of something. Finding something potentially harmful doesn't make a situation harmful. Water, table salt, sunlight, spices and herbs are also toxic in the right dose. So rather than upsetting people and wasting research dollars finding "toxins" why not devote those resources to discerning tolerable versus intolerable levels of exposure?


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