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Posted By Lisa Cawley
Hi all,
I have a question for ye. Can chairs with wheels be used in a lab if the wheels have a semi brake resistance on slip resistant floor? The workbenches are at normal office desk height.
Thanks,
Lisa.
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Posted By Taff2
Quick response is yes - spoke to our lab manager a few minutes ago & he stated that we've had them here for over 10 years - without incident. Team are well behaved and do not have a F1 track in the lab!!!
Can I hi-jack your thread and ask the question of having emergency gas shut off valves / systems for bunsen burners in labs - factories, schools or colleges. Is there a need? or are the flames unlikely to cause major fires? We generally keep other combustibles well away from the area.
If the shut off valve is 15m away - how long would the flame last before running out of fuel (standard diameter 1/4" pipe).
How big would the flame be?
Any good sources of advice / guidance on this?
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Posted By Julian Meer (at Work)
At the risk of hijacking Lisa's thread further, but hopefully offering advice to Taff2.
1. The average duration of burn out can be calculated from the gram-moles of gas within the system (= PV/ RT (from ideal gas equation))divided by the burn rate for the bunsen burner (as specificed by the manufacturer)( t = n * RMM / burn rate (g/s)). This is an average since the pressure drop within the system will be a differential (there are other eqautions for this based on standard chem eng fluid dynamics). In practice the flame will go out before this once the content of the fuel in the flame drops. Which for methane is about 15% (but don't quote me).
2. There are equations for estimating jet flame size for larger releases, however, you already know this - it is the size of the flame when in diffuse mode (bunsen valve closed / yellow flame) with normal supply pressure behind it. The jet flame size will diminish with time as the pressure drops (again differentially) within the system down stream of the isolation valve.
3. Calculate if you want, but I would approach this pragmatically. Ensure you have an adequate isolation valve clearly labelled and accessable - close but out of the danger zone. The mechanical isolation valve for the system maintenance should suffice in my opionion in an emergency (check from time to time is isn't passing). Process plants often have hard-wired emergency isolation valves, e.g., ROSOV's, but I don't think you'd need to do that for the lab.
4.I also know of one lab fire from an unattended bunsen. (Sorry, tongue-in-cheek) I believe all flames can cause major fires (see legend of prometheus and great fire of London).
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Posted By Robert.
Lisa,
I preferred your question, easier to answer.
Boo to the thread hi-jackers.
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Posted By Merv Newman
Lisa,
trying to de-hijack your thread for you.
I worked, after leaving school, in a lab that only had stools. Most awkward but got used to it. Then they built us a brand new lab and it came equipped with wheeled chairs. Wheee !
We could scoot from the fume cupboard to the bench and the teapot and back again without standing up ! (microbiology lab)
Must admit that the chairs were wipe-clean-disinfectable. Though I can't remember anyone bothering.
Wheeled chairs in a lab ? No problem for me.
Merv
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