** Q.One of the toxicology slides shows that oxygen can be toxic at 50-80% of air.  Does the exposure under these circumstances need to be chronic for toxicity to take place? or perhaps just longer than a few minutes or hours?  For example, i've heard of "oxygen bars" which from my understanding people just breath high percentages of oxygen.  I assume there are not any toxic effects from doing this or else the practice would be banned?
A. In Europe for many years they had radium bars, like a mud bath, where people would sit in a bath and get warmed by radium salts.  Acute oxygen toxicity occurs in divers when the oxygen gets over two partial pressures and results in convulsions.  The book was talking about chronic oxygen toxicity and involves inflammation of the respiratory tract by people on oxygen therapy.  Used to be they put people in “oxygen tents” of pure oxygen, which caused that problem.  Now they give people much less O2.


**Q. This relates to the previous question in that, it seems like the definitions toxic, hazardous, waste, etc, keep getting more and more legalistic almost to the point where the general public has a completely different understanding of the topic than the scientific community involved with the legal debates.  If public safety is the ultimate goal (perhaps I am wrong about this) than shouldn't the definitions of poison, toxic, and hazardous that are used for the legal regulations be adjusted to more closely relate to the general public's "perception" as to what is toxic etc?  I understand that this would pose a large problem in being able to legally define these terms because human "perceptions" are often very different from person to person and at times can be wrong but if the intent of the laws and regulations are to protect the people than shouldn't the people be able to easily understand them?
A. Here’s a lesson from another course that deals with your question in detail:

Q. Will you leave all the modules posted on Blackboard throughout the semester? Or will you pull them off as you add new one's?
A. Yes.

A. Deep questions, but so deep, I can give shallow answers. The abstract about the candles presented no quantified health risk for the candles. The author did a chemical analysis of soot and other combustion products from a set of very different candles, and not unsurprising found different chemicals. Then the author presented the health effects from stated levels of these chemicals, where they were known. For the biggest issue, candle soot, there were no known health effects published, so the author used the data from diesel exhaust, a completely different compound. What the author presented were assumptions stacked on top of estimates over a layer of extrapolations. We will often see this. My guess is the original paper carefully stated all this. When you use the words "serious health risk" you are trying to determine the acceptability of the risk. In my house, the fire danger from candles is thousands of time greater than any likely health effects.

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