Potassium piece, size limit?

I have quite an "adventurous" teacher who keeps asking for larger potassium pieces to react with water, which is actually becoming a concern given he has had quite a few near misses so to speak...
I checked the potassium metal hazcard and safer reactions documents but there is no recommendation of approximate size.

Thanks
 

STEMTech

Dave
We use a piece about the size of 2 grains of rice. I guess if the teacher want to use more, you can only advise, and he should risk assess.
 
Teachers cut it, so it's their problem to follow the SRA, they are supposed to talk about the hardness cutting it etc.
 
Like Paul, I just give the teacher the bottle and they decide how big a chunk they want to put in.

If they haven't done it before I'll show them what size I think should be used.
 

paul r

COMMITTEE
I had a horrible SLT member of staff, science teacher for a very long time . have a piece jump out hit the ceiling and burn the desk . The kids loved it ! Luckily I heard the screams of laughter and sorted situation out . Afterwards, I calmly asked if they had done a risk assessment ( none) so, reported accident to the health and safety officer
 
3-4mm is sufficient. I have it ready cubed in small jars. A teacher once put in a big chunk, broke the trough, scared the living daylights out of the students and herself and caused a near breakdown for the H&S gnome. Don't take any chances now and it's us who clean up their messes.
 

karen b

COMMITTEE
We give a couple of pieces that are about twice the size needed with a scalpel to cut to size and a list giving the CLEAPSS recommendations. Unless it is the head of chemistry, she gets one piece the correct size
 
We also use 3mm for potassium. 4mm for sodium and 5mm for lithium.
Yes this is what CLEAPSS recommend. If I think the teacher is prone to use pieces that are too large I only give them small pieces and for the ones who just keep adding pieces till the water is deep purple I only provide one piece!
 
A course I went on told about a piece of sodium jumping out of a trough - bouncing a few times and then going underneath a pair of safety goggles and burning a student just under the eye.

Na size, safety shield, goggles correct distances were all right - just a huge freak accident.

I always stick to the 5, 4 and 3mm rule.

If they want a larger piece - separate RA - done outside by remote method = speak to HOD & Head of school.
 
we give small chunks in bottle labelled "large pieces to be cut before adding to water" (as a clue :p), together with the CLEAPSS risk assessment. Never had a problem here. We also have a perspex lid for our trough and give 2 safety screens also.
 
Teachers cut it, so it's their problem to follow the SRA, they are supposed to talk about the hardness cutting it etc.
We supply it already cut in containers... but your comment made me think that the students won't get to learn about the cutting aspect (i.e its properties)
 
I had a horrible SLT member of staff, science teacher for a very long time . have a piece jump out hit the ceiling and burn the desk . The kids loved it ! Luckily I heard the screams of laughter and sorted situation out . Afterwards, I calmly asked if they had done a risk assessment ( none) so, reported accident to the health and safety officer
I can imagine they learnt they lesson?
 
I provide a bottle of pieces I've cut to the max I want out (about 5mm square), what they do with that is up to them. Had a teacher who went for it and we had to remove the metal from the ceiling tile!
 
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