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[*] posted on 10-3-2019 at 10:10
Questions about chlorine safety

Hi, I was wondering if there are any tips from you guys about safety when using chlorine gas. I plan to do a couple projects that involve chlorine gas and I was wondering if there is anything that I should know about safety. I plan to do it outside with a respirator and safety goggles, but I just want to make sure there’s nothing that I’m missing.
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[*] posted on 10-3-2019 at 10:22

Prepare some sodium sulphite/thiosulphate solution for spills.

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[*] posted on 10-3-2019 at 12:11

IMO if this is not frequently repeated and you have good ventilation then you will be OK - even without a gas mask

Although chlorine gas is very toxic, (a war gas / chemical weapon)
at hobby-level concentrations and exposure levels (other than major accidents)
you will run away from harm long before there is real danger due to the eye-watering choking-ness of chlorine gas.
This is based on multiple personal exposures over recent years,
but I'm old and a smoker,
- if you want to be 'safe' then ignore this comment ;)

Make sure that the cartridges for your mask are suitable and the mask has an airtight seal to your face.

In general always have an appropriate 'antidote' available.
My 'favourite' for outdoor work is a garden hose pipe operated at the nozzle end for immediate use.

Chlorine gas is really good at corroding metals - Keck clips, water taps and sinks included :)

[Edited on 10-3-2019 by Sulaiman]

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[*] posted on 10-3-2019 at 12:23

Assuming you will generate chlorine from an oxidizer and hydrochloric acid do not assume they all act the same. I have not had any troubles with chlorine gas but i have made sure to work with it on windy days but it is probably not necessary. It is a heavy gas though.
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[*] posted on 26-6-2019 at 05:07

Apologies for resurrecting an older post, but I thought it might make sense to keep chlorine discussions together...

In the past when I have made gas apperatususeses I've used good ol' black rubber stoppers and soda lime glass tubes to connect it all together. This has served me well in the past. I'm a bit concerned about the ability of the stoppers to hold up against Cl gas, or, while I've never had an issue with it before, one popping if the pressure gets too high. Am I being overly cautious, or does this sound like an unpleasant learning experience waiting to happen? Any recommendations? (I know it would be cheap enough to get some glass connectors, but I'm getting tired of my wife rolling her eyes at me whenever I get another package from China with "fragile" stampped all over it...)
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[*] posted on 26-6-2019 at 08:14
Personal opinion :

Dry chlorine gas will attack rubber, if moisture is present it works much quicker,
but I would not expect the bung to loose its integrity for hours or days.
If pressure builds up it can pop open a ground glass joint easier than a well seated bung,
So, do not let the pressure build up ... ever.
Often the only requirement for pressure is when bubbling through a liquid
and that requires a pressure of only a few inches of water, a few mmHg,
(the depth of the bubbler output)
Unless you use a diffuser (glass or ceramic frit) which needs a little extra pressure.

IF bubbling chlorine through a liquid is expected to form a precipitate then I advise some kind of alternative pressure release mode,
as the precipitate can form in the frit, or even in an open ended glass tube - blocking the gas flow.

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[*] posted on 26-6-2019 at 11:29

The only major trouble I have had with generating small volumes of Cl2 occurred when I added the WRONG concentration of an acid to chlorine bleach!

The acid was H2C2O4, and in addition to the exothermic and rapid reaction producing chlorine gas (in what I would described as a nearly uncontrolled eruption), an unexpected (on my part, as I wasn't planning on using this acid) large volume of CO2 mixed with Cl2 also occurs (from an apparent triggered decomposition of the excess Oxalic acid).

Very scary....

A reference as cited previously on SM:

Quote: Originally posted by AJKOER  

Per this source: "A dictionary of chemistry and the allied branches of other sciences", Volume 4, by Henry Watts, page 250.

"Chlorine does not act on dry oxalic acid; but in presence of water, decomposition quickly takes place, thus:

H2C2O4 + Cl2 = 2CO2 + 2HCl

A similar reaction is produced by bromine, hypochlorous acid, and the chlorides of easily reducible metals. Hence oxalic acid precipitates metallic gold from auric chloride, especially on boiling;"
[Edited on 27-8-2018 by AJKOER]

My expanded take of the reaction system, for those interested:

2 NaOCl + H2C2O4 --> 2 HOCl + Na2C2O4 (s)

NaCl (also found in bleach from its creation by the action of Cl2 on say aqueous NaOH), leads to HCl:

2 NaCl + H2C2O4 --> 2 HCl + Na2C2O4 (s)

2 [ HCl + HOCl = Cl2 (g) + H2O ]

H2C2O4 + Cl2 (aq) --> 2 HCl + 2 CO2 (g)

H2C2O4 + 2 HOCl --> 2 H2O + 2 CO2 (g)

2 [ HCl + NaOCl --> HOCl + NaCl ]



However, with proper dilution with Fe/Mn ion rich tap water, in the presence of a hard surface transition metal (like Fe or Cu), I may expect some powerful radicals created to greatly increase cleaning power. Here is a supporting comment:

"All I know is when I was a kid we would run clorox through the pressure washer and go through 10 bottles and cover a house with it. As far as oxalic acid goes, I perfer it over hydrochloric when removing staines on yachts and boats. Its truely amaising how, If applied correctly can turn a hunk of yard trash boat into a gistening white gem. Just got to de oxadise and wax and your sitting pretty" at .

This likely occurs, in my opinion, due to a fenton-type reaction between complexed Ferrous (via oxalate) and HOCl:

Fe(ll) (as a soluble complex) + HOCl --> Fe(lll) + .OH + Cl- (pH > 4.88)

with the powerful hydroxyl radical capable of breaking stains and such. The iron oxalate salt together with Mn can also be a potent photocatalyst (see, which in strong light rich in UV (near oceans/rivers), could further add to the bleaching effect.

Caution: Before working or experimenting with Iron Oxalate, please review this MSDS at .

[Edited on 26-6-2019 by AJKOER]
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[*] posted on 26-6-2019 at 14:43

Safety with Cl2 begins with producing it in a measured controlled fashion.
A pressure-equalising addition funnel is a must in my opinion. Then you can produce gas at the rate you need and keep control of the pressure. At any given time you only have the volume of the apperatus in Cl2 as a hazard.
I use TCCA and HCl. There seems to be little need to deviate from this recipe. Taking the time to work out your stoichoimetry is also a good idea. Then you know how much gas you have produced: which is also good for monitoring your reaction.

A scrubber is mandatory. Concentrated NaOH works fine in my experience. A suck-back trap is also good practice. Scrubbers protect both you and your environment.

Outside in the wind would be sensible if you don't have a fume hood. But with good scrubbing you may not even smell much.

Respirator is useless unless you have filters designed for chlorine. Even then it might be superfuous. The good thing anouty chlorine is that the discomfort level is well below that danger level. You will run away with streaming eyes and burning throat before you encounter significant danger. And then you know you are liberating gas. If you are wearing a respirator you might not know that the gas is escaping in an uncontrolled fashion.

Biggest exposure is likely to be when you pack down your apperatus. Think about how you will do this. If you can neutralise the gas without releasing any, that would be best.

Good idea to have something on hand to neutralise spills or accidents. I have a spray bottle with thiosulfate solution in my lab that is always close by when working with oxidants.

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[*] posted on 27-6-2019 at 23:51

I fully agree on the point of well controlled production rate of the gas being of utmost importance. A runaway reactor can quickly generate dangerous levels of chlorine if no adequate ventilation is available. So care is advised to think the construction through and have failsafes operational if a mishap should occur.

Carbon based filters in a gas mask will be totally fine to absorb chlorine. Oxalic acid solution is also rather effective against neutralising spills. We used to call it "antichlor" back in the days.

As for the toxicity, not really too bad unless one encounters a serious concentration (like a sealed room that has been filled by a leak from generator or gas bottle). Also I must note that higher concentrations of chlorine tend to provoke an involuntary inhalation reflex, which may cause an infortunate and careless experimenter to get a good deep breath of the poison.

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[*] posted on 20-7-2019 at 21:30

-1500 ww1 vets who had suffered severe chlorine exposure were followed for their entire lives, no long term health effects were noted on any of them.
That said the nausea it produces when you get a bit is horrible, nausea is just shit.
It's a heavy gas sinks and as such hangs about in pockets. There is no simple gaseous antidote you can spray to neutralise it, only aerosols of solutions already spoken for. As such I find large flat trays of naoh solutions do a fairly ok job.
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[*] posted on 21-7-2019 at 06:05

Quote: Originally posted by fusso
|| Prepare some sodium sulphite/thiosulphate solution for spills.

prepare some 5% bicarb wash for the eyes!, if a small waft gets in the eyes it can burn like an sob for a while the bicarb wash makes the missery go away much faster!

Don't sniff the tube to see if it is working (When yunge I only made that error once!)

I've handles cylinders of chlorine, worked around it a few times, and made crap loads of it, it really isn't that scary at the levels we use it at, very unpleasant yes! Respect it but don't fear it.

Use good lab practices, have 500ml of bicarb wash for the face and eyes if you get a puff of it and get discomfort that wash helps a good deal, plan it all out and be methodical and you will have 0 issues.

[Edited on 21-7-2019 by XeonTheMGPony]
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[*] posted on 22-7-2019 at 06:03

My biggest accident with chlorine was mixing a large quantity of hydrochloric acid and hydrogen peroxide for the purpose of glassware cleaning. After some time there was a pressure developed in the bottle and I poured it down the drain. It is hard to make the same way it is hard to make with ammonia - you just want to run out of the room. So, if you know how to swim under water the technique is just the same - stop your breath till you can leave the room.

So, I think the most danger is when the chlorine concentration is raised too rapidly and your nose is very close.

I would use a closed system and ground glass joints (with clamps) as much as possible. Also to prevent leaks and to make possible to easily disassembly the apparatus I usually always apply suction from a water pump. When the pressure in all part of the apparatus is lower than outside there will be minimal leak even if you detach some part for few seconds. The same way you can empty the apparatus - just make the maximal suction and open the opposite part of it. After several minutes the air will replace most of chlorine inside. Put the scrubber (mandatory) before the pump, use 2 flasks to allow gas flow in both direction and put an empty bottle between the pump and the scrubber to prevent leaking water from the pump. Just after disassemble (best to do it in front of a fan) fill the water in all parts of the apparatus to be sure no gas was left inside.

Also, try to fix all parts, not holding anything in hands in case you need to escape. Prepare the ventilation so you will be able just turn it on while escaping.

If you use a new glassware or parts, especially with heating, do it only after using the same apparatus with less toxic/irritant gas before making more dangerous experiments. This is also important, because sometimes pressure is distributed not as you expected, so test everything before. Making simplest proof of concept with HCl + Na2CO3 can give you idea how you can manage the gas flow.

Don't sniff any parts of your apparatus and joints - there is always a small leak in places where hoses are connected, so avoid put you nose on it.

Also, obviously, but very important. Make sure the material your hoses are made of is resistant to the gas.

Of course, use good googles, because chlorine can attack you through eyes too.

Actually I use the techniques I described for working with H2S.

There is some important aspect which is different with different gases - you should always think about reaction of the gas with liquids. For example, some gases are develop negative pressure dissolving in water (NO2) or reacting with scrubber (NH3 + HCl). This is often unforeseen and if you made all other precautions this behavior could be most dangerous.

[Edited on 22-7-2019 by teodor]
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[*] posted on 27-8-2019 at 23:34

ammonia is really neat for handling volatile acidic compounds, you can neutralize it in the air
avoid breathing anywhere near containers that may contain chlorine, with just minor exposure you will have at least one very terrible day, its very reactive. i got a bottle of sodium chlorochromate, it generates small amounts of chlorine over time. its made by adding excess HCl to NaCrO4, anyhow when this bottle is opened, the chlorine can be felt warming your skin as it reacts with your cells, no visible effects of this but its quite spooky if you think about it.

~25 drops = 1mL @dH2O viscocity - STP
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[*] posted on 28-8-2019 at 00:18

I've poisoned myself with chlorine gas once.30ml of pool chlorine and 20ml of gaa is more than enough to cause symptoms such as a throbbing headache and vision problems like your starting to go blind.a large dose of codeine and fresh air for an hour or two before I started feeling better.was fine by the next day.the bathroom extraction fan on the roof was not adequate for the small reaction on the floor even with the window open.this stuff is definitely a poison deserving of war gas status.
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