Safety in the laboratory for a teacher has three main strands:
Safety at the planning stage
For each lesson fill out a risk assessment. In the Physics Handbook the potential hazards of equipment is listed - hazards are anything that could reasonably go wrong - chipped glassware is more likely to cause an accident than exploding chemicals or a child drinking acid simply because it gets overlooked - heavy equipment can be dropped - electrical equipment might have faulty wiring etc.
Think... do you need safety goggles? Not only for heating things or noxious substances but they protect agains sharp implements etc. It is better to have them when not needed than to not have them and have a child poke its eye out or rub iron filings in it!
Think... do they need lab coats? For all biology and chemistry practicals lab coats are vital but only 'messy' physics need them - warn the girls in advance to bring them to the lesson. If you forget you can put a note in their register the day before.
Think through the stages of the experiment that your pupils are going to carry out in the context of the group. Some pupils are safety conscious - they handle delicate and/or potentiallly harmful equipment with great care - others might deliberately cause problems and/or drama in your class. At WGHS we have sensible girls - but some girls have not got much common sense. Caring parents sometimes prevent their daughters from even striking a match - we then expect them to light a spill, carry it across a lab and light a bunsen burner! Do not plan to rush through the safety reminders before a practical session. Ensure you leave time in your plan to go through the warnings and precautions.
Think about the activity - is it for individuals or does it lend itself to group work? If so what size group? This will affect your equipment order (you need to check whether there is enough equipment available for small groups before you plan further).Then you need to think about how the pupils are going to be split into groups. If you leave them to it, they will divide into friendship groups - uneven sized groups and some might get left out! Often you can get them to work in 'tables' - but watch out for unequal grouping - move students to get even sized groups. Another possibility is to number the form (most at WGHS already know their register number) and divide them up accordingly by number. The smaller the group size the less likely that someone will be 'left out' - but the more groups you need to get round.
Think about the lab layout in the context of the number/type of pupils you have to teach. Where should they work - do they need sinks, gas, electricity etc. Will they have ease of access to utilities - or will there be a rush to one end of the lab? When you order equipment you can ask for it to be put around the lab - you can be specific ast to where it should go. Equipment needs to be accessible but widely spaced so that different members of the group can fetch different items.... and at the end of the lesson put them back neatly.
How are they going to know what to do? A clear worksheet or PowerPoint slide with instructions on it needs to be prepared before the lesson. Then you work through it - imagine yourself as a pupil - is there enough information - is it simple and clear? Most practicals are 'generic' in that a good worksheet will serve you in many posts - the computer document can easily be tweaked to fit the new school's equipment. The worksheet is also useful to the technician - it helps if they know what you are going to do!
Safety during the lesson - before the practical activity
You are responsible for the safety of the pupils.You should instruct them how to keep safe in the lesson every time you teach them.Get into the habit of talking through what they have to do - talking through possible risks as you go. Write the key points on the board to emphasise them. You don't have to do all of the talking - use Q&A to check their awareness of potential hazards. Praise them for remembering safety points from previous sessions/experineces. Encourage them to regard practicals as potentially hazardous but totally safe if performed correctly... and for being able to work safely as mature and laudable - they will need to be able to do that in the workplace!
Always start with the lab layout - get the bags put out of the way, stools tucked away - make sure they understand why they need to be standing during the practical session. Even carrying the equipment can be a hazard - some equipment comes apart if carried in a casual manner - show them the problem (e.g. lenses falling out of rayboxes), some equipment is easy to knock off the bench - thermometers roll off easily, beakers with thermometers standing in them are easy to tip over etc. Point out the danger of tripping over trailing electrical wires if they have to plug equipment in etc. They should be able to tell you most of the dangers - it is a life skill they need to develop for the workplace - but remember many of them have been protected from potential hazards and may not think ahead enough!
Instruct them to work as quietly as possible so that you can keep control of the goings on. Explain that you need to be able to ask for their attention and to hear their calls for assistance. They get excited when doing a practical - don't let that excitement descend into anarchy! You must be in control - set the tone before the practical.
Send individuals from each group to collect equipment - check everyone has the correct equipment and knows what to do.
Safety during the lesson - during the practical activity
This is the most taxing part of being a science teacher - most other subjects do not have this sort of pressure. You have to be aware of everything that is going on. You cannot allow the noise level to get too high - they need to hear your instructions and you need to hear calls for assistance.
You need to circulate and check that all groups are coping (and allowing all members of the group to contribute). Use Q&A to check they understand what they are doing and most importantly 'why'! - too many students have a science lesson with lots of fun activity that it pointless to them because they cannot see why they are doing it at all! At WGHS we want the students to understand the point of all activities - even if the point of the activity is to highlight how difficult it is to get reliable (repeatable) results. Do not allow yourself to become too engrossed with the group you are with - you need to use the 'eyes in the back of your head' to be aware of everything that is going on around you.
When I started teaching it was considered to be unsafe to have more than 20 pupils doing practical work in a lab - now you can have up to 30 to cope with! The physics labs were built for 20 pupils (P3 was a prep room) and even the new science block had labs built for 24 pupils - our class size is usually 27 That is a big responsibility - you need to be totally aware - don't ever be tempted to 'let them get on with it' and do some marking. If the practical is very undemanding there could well be 'social disruption' betweeen the pupils - easy to miss if there is noise and a teacher engrossed in something else - or even worse not there!
Don't EVER leave a classroom when a practical is going on or there is equipment around the lab. If you need assistance send a pupil to get help from another member of the department and/or telephone for assistance from the prep room (keeping the door open). As a student this will not apply - but in your first post it may well come up!
Keep an eye on the time. You have to leave the lab in a suitable state for the next teacher - equipment stacked neatly, benches cleared/wiped. If it didn't go according to plan cut your losses - next lesson can be an autopsy of this lesson - with you doing a demo of the practical if necessary and/or handing out a set of results they can work from. In this way you progress - students can often learn as much from a practical that goes wrong as from one that is 'perfect'. You just have to put the correct 'spin' on the experience.
Click here to go to the topic safety page - it leads on to a subject specific section that will help you identify risks when ordering particular types of equipment..
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Always start with the lab layout - get the bags put out of the way, stools tucked away - make sure they understand why they need to be standing during the practical session. Even carrying the equipment can be a hazard - some equipment comes apart if carried in a casual manner - show them the problem (e.g. lenses falling out of rayboxes), some equipment is easy to knock off the bench - thermometers roll off easily, beakers with thermometers standing in them are easy to tip over etc. Point out the danger of tripping over trailing electrical wires if they have to plug equipment in etc. They should be able to tell you most of the dangers - it is a life skill they need to develop for the workplace - but remember many of them have been protected from potential hazards and may not think ahead enough! 
lesson with lots of fun activity that it pointless to them because they cannot see why they are doing it at all! At WGHS we want the students to understand the point of all activities - even if the point of the activity is to highlight how difficult it is to get reliable (repeatable) results. Do not allow yourself to become too engrossed with the group you are with - you need to use the 'eyes in the back of your head' to be aware of everything that is going on around you. 
When I started teaching it was considered to be unsafe to have more than 20 pupils doing practical work in a lab - now you can have up to 30 to cope with! The physics labs were built for 20 pupils (P3 was a prep room) and even the new science block had labs built for 24 pupils - our class size is usually 27 That is a big responsibility - you need to be totally aware - don't ever be tempted to 'let them get on with it' and do some marking. If the practical is very undemanding there could well be 'social disruption' betweeen the pupils - easy to miss if there is noise and a teacher engrossed in something else - or even worse not there! 
Keep an eye on the time. You have to leave the lab in a suitable state for the next teacher - equipment stacked neatly, benches cleared/wiped. If it didn't go according to plan cut your losses - next lesson can be an autopsy of this lesson - with you doing a demo of the practical if necessary and/or handing out a set of results they can work from. In this way you progress - students can often learn as much from a practical that goes wrong as from one that is 'perfect'. You just have to put the correct 'spin' on the experience.
