Rank: Forum user
|
we have a substance used on site called Anchorspray:
Dichloromethane - 15 mins TWA - Limit (ppm) - 300 - Limit 1060 (mgM-u) Dichloromethane - 8 hrs TWA - Limit (ppm) - 100 - Limit 350 (mgM-u)
The EH40/2005 states 1,1-Dichloromethane - CAS Number - 75-34-3 - ppm 100 WEL Long term exposure limit (8-hr TWA reference period)
We use this substance for a max of two hours a day but in 10 minute intervals
How do we calculate the ppm of 100 over an 8 hour period to ensure that we do not exceed the limits?
|
|
|
|
Rank: Super forum user
|
EH40 used to set out the method (page 50/51 or thereabouts as I recall -but that was the 2002 edition). You haven't mentioned the concentration of the dichloromethane in that product. It's nasty stuff.
|
|
|
|
Rank: Super forum user
|
If you are spraying then presumably you will also have to consider skin exposure, for which there is no WEL. For dichloromethane the majority of gloves provide only splash protection. For example even a relatively thick nitrile gauntlet will only provide around 10 minutes permeation breakthrough time, the thin, single use nitrile less than one minute. The best glove for this substance is Viton, but even this will only give you around 4 hours permeation breakthrough time (max) and at around £70 per pair this will get expensive! (Note that the permeation breakthrough time start from first contact and continues, even when the glove is not being used, so for an 8 hour shift with the exposure as described you would need at least 2 pairs!) Chris
|
|
|
|
Rank: Super forum user
|
Dichloromethane - yikes, I would really consider another material for your process, particularly if spraying the product But if you can't change material at present there is some detailed guidance for paint-stripping processes at the HSE, download this: http://www.hse.gov.uk/pubns/wis19.pdfAlso known a Methylene Chloride, or DCM, it is a Category 3 carcinogen, which means 'possible' carcinogen, in that it has some effects that are of concern, so you really need a local ventilation system and I would NOT rely on 'caculating' ppm exposure; you need an effective meter/detector method of monitoring ppm in the workplace atmosphere to ensure the local ventilation is always effective. JohnW
|
|
|
|
Rank: Super forum user
|
If it's the paint stripper you are using, you need to think about the methanol exposure, too! Although one can calculate what the exposure can be permitted to reach during two hours exposure in an eight-hour day, you will need to measure the exposure as well to ensure that there is adequate control. Don't forget that you will need to comply with both the long- and short-term limits.
LB
|
|
|
|
Rank: Super forum user
|
Before we get too far, please check what substance you actually have. Four separate names have been used so far on this topic, and they relate to two completely different chemicals.
Dichloromethane Cas no. 75-09-02 Methylene chloride, also Cas no 75-09-02 empirical formula CH2Cl2
1,1- Dichloromethane - does not exist. The reason is that this is also dichloromethane and it does not require the 1,1- designation as the chlorine can only be in one place in this molecule.
however, 1,1- Dichloroethane does exist and is Cas no. 75-34-3, empirical formula C2H4Cl2
Which one do you have?
|
|
|
|
Rank: Forum user
|
Jane Blunt wrote:Before we get too far, please check what substance you actually have. Four separate names have been used so far on this topic, and they relate to two completely different chemicals.
Dichloromethane Cas no. 75-09-02 Methylene chloride, also Cas no 75-09-02 empirical formula CH2Cl2
1,1- Dichloromethane - does not exist. The reason is that this is also dichloromethane and it does not require the 1,1- designation as the chlorine can only be in one place in this molecule.
however, 1,1- Dichloroethane does exist and is Cas no. 75-34-3, empirical formula C2H4Cl2
Which one do you have? I have Dichloromethane Cas no. 75-09-02 - >25% <50% Concentration ranges
|
|
|
|
Rank: Super forum user
|
SPR wrote:
I have Dichloromethane Cas no. 75-09-02 - >25% <50% Concentration ranges
So what is the balance? This could be important, as pointed out by Leadbelly.
|
|
|
|
Rank: Super forum user
|
Irrespective, I'd put serious effort into finding an alternative. If the OP can share the industry/ process, there may be others here who can suggest suitable alternatives.
|
|
|
|
Rank: Super forum user
|
Another item of essential information is how you are spraying this. Is it using an aerosol can? If so, what is the propellant? This could have a bearing on both the airborne exposure and the skin exposure.
Also please note that the information on gloves that I posted relates only to the single substance. Once you start to deal with mixtures it gets very much more complicated. For example I can show you a glove that with each of toluene and methanol has a permeation breakthrough time (according to the EN374-3 test) of >240 minutes but when used against a 1:1 mixture of the two the permeation breakthrough time drops to 9 minutes!
You will also need to train the glove users so that they do not contaminate their hands when removing the gloves. This is a common problem. It is not uncommon when training to find that over 50% of glove wearers contaminate their hands when removing their gloves, even though they have been shown how.
Chris
|
|
|
|
Rank: Forum user
|
|
|
|
|
Rank: Super forum user
|
Purely from a theoretical perspective, and to try and answer the original question, and assuming this is a classroom based theory question rather than getting involved too deeply in assumptions about worker health, morals and the carinogen directive etc etc....:
The TWA is an 8 hour average Actual usage is 2hours per day Assumption is that remaining 6 hours exposure is 0ppm
So based on the 8hour TWA the maximum would be:
400ppm x 2hours / 8hours = 100ppm 8hr TWA
So theoretically you could be exposed up to 400ppm for 2hours in an 8hour period which gives the TWA of 100ppm but of course this exceeds the 15minute STEL, dosn't it???
But wait....
You are only using the material for 10 out of that 15 minutes, averaging this out over 15minutes means that your 10minute exposure can be up to 450ppm to still not exceed the 15minute STEL assuming 0ppm for the other 5 minutes. Because...
450 x 10mins / 15mins = 300
Sooooo theoretically, im speaking theoreticaly here....
Yes you can be exposed to 400ppm for 2 hours a day in 10 minute intervals.
Des
|
|
|
|
Rank: Super forum user
|
You need to have an estimate of the exposure, preferably by actual air monitoring as the exposure will be dependent upon the technique used, including any general dilution ventilation, LEV or spray booth and that need to be taken into account.
|
|
|
|
Rank: Super forum user
|
Just a further note of caution and clarification to Descarte's theoretical response at #12 above.
In practice, this would be contrary to Regulation 7 of the COSHH Regulations.
|
|
|
|
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.