# How safe is bleach to use? **URL:** \ **Category:** Factual Questions\ **Created:** [June 6, 2012, 6:55pm UTC](https://boards.straightdope.com/t/how-safe-is-bleach-to-use/624301 "2012-06-06T18:55:13Z")\ **Posts on this page:** 9\ **Page:** 4
**Author:** ![VOW](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/vow/32/3043_2.png) [@VOW](https://boards.straightdope.com/u/VOW)\ **Post date:** [June 9, 2012, 2:07pm UTC](https://boards.straightdope.com/t/how-safe-is-bleach-to-use/624301/61 "2012-06-09T14:07:27Z")
> [@Waterman](#): > > Vow you have made my day! A little off topic perhaps but let’s talk about phenolphthalein for a brief moment in an amusing anecdote. > > When I was a freshman in college (don’t ask how long ago that was) several of my senior fraternity brothers stole some 95% ethyl alcohol from our school chem lab and thought they had struck the mother lode! They heartily drank it down without knowledge of the fact that the school had denatured the stuff. Well this could have been catastrophic if the school had used methyl alcohol or some other really nasty stuff to denature with but they chose to denature it with phenolphthalein! Which brings us to the second great use of phenolphthalein! Besides it’s use as an indicator in laboratories for acid-base titrations , it is (was) the main ingredient in Ex-Lax. You can imagine the fun-filled 12 hours that the two brothers had!!! I had heard that frat boys liked to sneak phenophtalein into punchbowls at parties. If you could find a really DARK punch (something at Halloween, maybe?) then methylene blue was another good adulterant. They always have a lot of worried kids at Student Health Service the day after a methylene-blue-spiked party! BRILLIANT idea of the lab supervisor to denature the ethyl alcohol with phenophtalein! I’ve heard that it is usually denatured with benzene, and that would make for some very sick (and probably hospitalized!) frat boys! ~VOW ---
**Author:** ![OldOlds](https://avatars.discourse-cdn.com/v4/letter/o/a3d4f5/32.png) [@OldOlds](https://boards.straightdope.com/u/OldOlds)\ **Post date:** [June 10, 2012, 1:36am UTC](https://boards.straightdope.com/t/how-safe-is-bleach-to-use/624301/62 "2012-06-10T01:36:06Z")
> [@GameHat](#): > > I’m not an expert on cleaning and disinfecting, but I am a chemist. So I gotta ask. Where’d you get the 200 ppm number? > > Not doubting you, just curious. And googling gives me a thousand different answers from a thousand different sources of varying authority. > > I did find a few sources that say a 1:100 dilution gives about 500 ppm, if that makes the envelope calculation quicker. For whatever it’s worth, when I worked in a diagnostic lab (lots of blood and urine- yum) we used a 1% bleach solution with 10 minute contact time to disinfect equipment and surfaces. That was about 15 years ago. ---
**Author:** ![Waterman](https://avatars.discourse-cdn.com/v4/letter/w/b2d939/32.png) [@Waterman](https://boards.straightdope.com/u/Waterman)\ **Post date:** [June 10, 2012, 4:15am UTC](https://boards.straightdope.com/t/how-safe-is-bleach-to-use/624301/63 "2012-06-10T04:15:45Z")
> [@OldOlds](#): > > For whatever it’s worth, when I worked in a diagnostic lab (lots of blood and urine- yum) we used a 1% bleach solution with 10 minute contact time to disinfect equipment and surfaces. That was about 15 years ago. I am curious as to what the lab may have purchased as its source of bleach (commercial strength or grocery store)? And also, was the bleach diluted to 1% strength by others and packaged? In drinking water disinfection for surface waters the main consideration is C[sub]T[/sub] for determing regulatory compliance with the concentration in mg/L of free chlorine residual multiplied by the time before the first downstream user. Needless to say that your C[sub]T[/sub] of 10,000 times 1 minute = 10,000 is much higher than the standards that must be achieved for drinking water compliance! ---
**Author:** ![Waterman](https://avatars.discourse-cdn.com/v4/letter/w/b2d939/32.png) [@Waterman](https://boards.straightdope.com/u/Waterman)\ **Post date:** [June 10, 2012, 4:18am UTC](https://boards.straightdope.com/t/how-safe-is-bleach-to-use/624301/64 "2012-06-10T04:18:28Z")
> [@VOW](#): > > I had heard that frat boys liked to sneak phenophtalein into punchbowls at parties. If you could find a really DARK punch (something at Halloween, maybe?) then methylene blue was another good adulterant. They always have a lot of worried kids at Student Health Service the day after a methylene-blue-spiked party! > > BRILLIANT idea of the lab supervisor to denature the ethyl alcohol with phenophtalein! I’ve heard that it is usually denatured with benzene, and that would make for some very sick (and probably hospitalized!) frat boys! > ~VOW A definite hijack but, if you don’t mind, when did you graduate as you sound like the same era as me - 1970 (B.S. Chemical Engineering)? ---
**Author:** ![VOW](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/vow/32/3043_2.png) [@VOW](https://boards.straightdope.com/u/VOW)\ **Post date:** [June 10, 2012, 4:26am UTC](https://boards.straightdope.com/t/how-safe-is-bleach-to-use/624301/65 "2012-06-10T04:26:10Z")
To **Waterman** : Graduated HS in 1971. I left UCLA in 1974 to get married. I was a frustrated pre-med, so I had to take general chemistry, biochem, biology, and comparative phisology. Also abnormal psych, which was a hoot. I got sidetracked with Life, and didn’t make it back. ~VOW ---
**Author:** ![Michael63129](https://avatars.discourse-cdn.com/v4/letter/m/3da27b/32.png) [@Michael63129](https://boards.straightdope.com/u/Michael63129)\ **Post date:** [June 10, 2012, 4:33am UTC](https://boards.straightdope.com/t/how-safe-is-bleach-to-use/624301/66 "2012-06-10T04:33:03Z")
> [@Spectre\_of\_Pithecanthropus](#): > > ETA: I checked the book, and it says “free oxygen” to be exact; possibly it was ozone that was meant. “Free oxygen” refers to atomic oxygen; that is, not part of any molecule, which is what I have heard to be the disinfecting agent. In fact, that is what Wikipedia [says](http://en.wikipedia.org/wiki/Bleach): > [@](#): > > Hypochlorous acid decomposes readily to atomic oxygen. This atomic oxygen acts as bleaching agent through oxidation. ---
**Author:** ![Waterman](https://avatars.discourse-cdn.com/v4/letter/w/b2d939/32.png) [@Waterman](https://boards.straightdope.com/u/Waterman)\ **Post date:** [June 10, 2012, 6:08am UTC](https://boards.straightdope.com/t/how-safe-is-bleach-to-use/624301/67 "2012-06-10T06:08:31Z")
> [@VOW](#): > > To **Waterman** : > > Graduated HS in 1971. I left UCLA in 1974 to get married. I was a frustrated pre-med, so I had to take general chemistry, biochem, biology, and comparative phisology. Also abnormal psych, which was a hoot. > > I got sidetracked with Life, and didn’t make it back. > ~VOW It seems that you have not been badly served by your choices. Glad to rekindle all those _fond_ memories of chemistry! ---
**Author:** ![Waterman](https://avatars.discourse-cdn.com/v4/letter/w/b2d939/32.png) [@Waterman](https://boards.straightdope.com/u/Waterman)\ **Post date:** [June 10, 2012, 6:42am UTC](https://boards.straightdope.com/t/how-safe-is-bleach-to-use/624301/68 "2012-06-10T06:42:35Z")
> [@Michael63129](#): > > “Free oxygen” refers to atomic oxygen; that is, not part of any molecule, which is what I have heard to be the disinfecting agent. In fact, that is what Wikipedia [says](http://en.wikipedia.org/wiki/Bleach): The Wiki article you reference with relation to “atomic oxygen” is a discussion of the decomposition of calcium hypochlorite which contradicts the decomposition path described by Cotton in my post #22. I see a difference in the citations regarding the action of sodium hypochlorite based bleaches between the scientific and the so-called “lay” texts. I do not recall any reference to the existence of “atomic oxygen” in any of my chemistry texts. I’m from Missouri so “ **Show Me** ”. ---
**Author:** ![OldOlds](https://avatars.discourse-cdn.com/v4/letter/o/a3d4f5/32.png) [@OldOlds](https://boards.straightdope.com/u/OldOlds)\ **Post date:** [June 10, 2012, 10:50am UTC](https://boards.straightdope.com/t/how-safe-is-bleach-to-use/624301/69 "2012-06-10T10:50:06Z")
> [@Waterman](#): > > I am curious as to what the lab may have purchased as its source of bleach (commercial strength or grocery store)? And also, was the bleach diluted to 1% strength by others and packaged? > > In drinking water disinfection for surface waters the main consideration is C[sub]T[/sub] for determing regulatory compliance with the concentration in mg/L of free chlorine residual multiplied by the time before the first downstream user. > > Needless to say that your C[sub]T[/sub] of 10,000 times 1 minute = 10,000 is much higher than the standards that must be achieved for drinking water compliance! We used a commercial grade of Clorox, I forget the concentration, and we produced the final solution ourselves. We went through so much bleach that our waste water was held and monitored so that it could be treated prior to discharge into the city’s system. We would occasionally be notified (internally, not by th city) that we were putting too much bleach down the drain. Not that there was anything we could do about it. The disinfection procedure was mandated by the management, and you were not allowed to deviate from it. [Previous page](https://boards.straightdope.com/t/how-safe-is-bleach-to-use/624301.md?page=3)