Actually cross-contamination is commoner than people think.  It isn't just HeLa but any cell line that grows quickly (like many mouse lines); so you do have to be careful.  Many journals now expect authors to say that identities of all human cell lines were verified.  

Obviously if some medium with a cell in it has landed on the working surface, it is not going to somehow climb into the next dish/flask.   But if you used suction or vigorous pipetting, there is a possibility of an aerosol -- tiny airborne spray droplets that might contain a cell.  A droplet might land in an open bottle or on your pipette.   For that, you just need to:

(1) use separate pipettes for different cell lines and separate containers of medium, and (2) run the laminar flow for a minute or so between cell lines -- about the time you'd take to wipe with EtOH anyway.  15 min is not necessary.

I would never work with more than one cell line at the same time in the flow hood.  It may take longer, but cross-contamination will trash the whole project.

Hi,

as long as it's not HeLa cells that are notorious for 'flying', we don't have any special precautions for working with different cell lines at the same time (my record was 10 cell lines in parallel, no way would I have been able to have 'quarantine time' in between).

My personal precautions are to never have two bottles open at the same time as I even work on them simultaneously. (Paying attention to changing pipetts and cleaning away any drops etc does not really need mentioning)

Maybe you can just forego the UV time and spray down the bench with EtOH to be sure and not work with the celllines simultaneously.

I agree with Victoria, as long as the cell lines aren't particularly prone to taking over things, a quick wipe down with EtOH between cell lines and keeping separate stocks for each should be sufficient.

cross contamination is a very rare mistake that researchers can do. Thus, cross contamination likelihood is very very low compared to contamination by microorganisms if not using the safety hood properly. 

Agree with above comments!

Same here - wiping with EtOH in between and always doing one after the other with separate stocks.

I am often working with different cell lines at the same time - and just take extra-care not to use the same pipet tips, and open one flask after the other - but in between I don't go for any UV light and when really working in a clean way without spreading any drops of medium - just some Ethanol in between is fine.

I keep different cell types on different 6-well-plates if possible, but sometimes even on the same plates, depending on the experiments - and I never got a cross-contamination because of this.

Actually cross-contamination is commoner than people think.  It isn't just HeLa but any cell line that grows quickly (like many mouse lines); so you do have to be careful.  Many journals now expect authors to say that identities of all human cell lines were verified.  

Obviously if some medium with a cell in it has landed on the working surface, it is not going to somehow climb into the next dish/flask.   But if you used suction or vigorous pipetting, there is a possibility of an aerosol -- tiny airborne spray droplets that might contain a cell.  A droplet might land in an open bottle or on your pipette.   For that, you just need to:

(1) use separate pipettes for different cell lines and separate containers of medium, and (2) run the laminar flow for a minute or so between cell lines -- about the time you'd take to wipe with EtOH anyway.  15 min is not necessary.

I would never work with more than one cell line at the same time in the flow hood.  It may take longer, but cross-contamination will trash the whole project.

I agree with Dorothy, in my lab we had an episode of cross-contamination with a breast cancer cell line (HCC1954) overtaking a slower growing one. I have always been recommended 15 minutes in between cell lines as well as EtOH, but if your laminar has UV, 5 minutes should be enough. It really isn't worth it to work with more than one cell line simultaneously, as Dorothy says this could ruin your work. My last recommendation would be to make sure your stocks are authenticated, you don't want any nasty surprises when the work is finished!

Dear Gabriel,

I agree with above all suggestions. Apart from few more points.

  Only one cell line should be handled in a bio-safety hood at any one time, and the workspace thoroughly cleaned between cell lines.

Dedication of equipment to single cell lines bottles and aliquots of cell culture medium and other reagents must be enforced.

Bottles and aliquots should be clearly labeled and never shared between cell lines.

 Waste pots must be regularly emptied and replenished with a disinfectant effective against both microbes and cell cultures

Hope this helps!

I agree definitely with Dorothy. Ideally you should handle one cell line at a time... When you have more than 10 cell lines this ideal is difficult depending on what kind of experiment you need to perform: my first suggestion would be to think at a time schedule when you actually thaw a new cell line: "when will I need to pass them, to change the media ... will it be at the same time as the others or not"..; If at some point there are not enough hours in a work-day to perform everything individually, I actually handle two to three cell lines at the same time and I am being extra careful as the other above said (well labelled bottles especially are critical)! But with only three cell lines, I wouldn't take the risk on having a cross contamination... 

Hope this actually helped a bit, Cheers. 

I agree with Dorothy and Vacamullu: we  can not be too careful in cross-contamination precaution. Above all that other researchers specified, I would mention that in every lab many researchers are engaged, so all the people should take care about cells and follow the same rules. 

A also think that cell lines should be checked periodically.

I agree that there should be extreme caution when dealing with different cell lines. I use 0.02% EDTA to rinse my cells (some people use PBS) and 0.25% trypsin in 0.02% EDTA to dislodge my cells. So for each cell line I have a separate bottle of media, trypsin/EDTA, and EDTA. That will go a long way to minimizing cross-contamination. However, I think the use of UV light between cell lines might be a bit excessive. There is always a danger of destroying the rubber seals and gaskets in a HEPA filtered biological safety cabinet by using UV light in the hood. If the seals on your HEPA filter are compromised, then you open yourself up to possible contamination issues. What we do in our facility is a good, thorough cleaning of the hoods surfaces with 70% alcohol between cell lines. Separate solutions and thorough cleaning with 70% alcohol would be my suggestion.

 I also totally agree with above comments...

Having spent virtually my entire working life in cell culture I would simply advise this. Do not worry too much about saving that 30 mins, (after all there is bound to be something to do in between like write ups etc). Far better to mention it to everyone you meet and use this as a way of illustrating just how thorough you are in avoiding cross-contamination. Moreover note in your lab book the  start and end times of each culture and decontamination procedure so that the impossibility of cross-contamination is permanently recorded. I don't blame you for seeking greater efficiency but establishing a practice that is physically impossible to corrupt, (even accidentally), is far more valuable. Sooner or later you will encounter circumstances under which everyone's practices within a work stream fall under suspicion because of contamination or an unexpected result somewhere. It's very helpful for everyone if you can point out that nothing untoward could possibly have occurred on your watch. Not only are you covered but you can ensure troubleshooting can swiftly be focused on where any problem really lies. 

I agree with the other responses saying the risk is too high working with cell lines together (in the hood at the same time) - even if you do not have problems doing this once, the risk increases every time.  For working with cell lines consecutively, the most important thing is to wipe the hood down well with ethanol and let it run for a few minutes between cell lines.  Not all labs use UV in their hoods, and it's worth noting that UV is not always effective if the globe has not been cleaned or needs changing.  And it is important to still test cultures (mycoplasma + authentication) - contamination is a risk that you can minimise through good practice, but the risk is never zero.