The following safety considerations are specific to the EM laboratories

Please note that the EM laboratories are for authorized personnel only and must be labeled as such. For general departmental safety information, please click here. A copy of the following safety information can be found on the notice board in the laboratory.
 

• General Laboratory Safety
• Liquid Nitrogen
• Ethane
• Laser
• Electron Microscope Emergency Shutdown
• Sulphur hexafluoride gas

General Laboratory Safety

• The laboratory COSHH form must be read and signed before any work can be done in the EM laboratories. This form is kept in the departmental office.

• Be careful with the stains used for Negative Stain microscopy. Uranyl Acetate is weakly radioactive, phosphotungstatic acid and ammonium molybdate are toxic, and sodium silicotungstate is harmful. Handle the heavy metal salts with gloves. Handle the powder gently to avoid creating dust and clean up the balance and bench areas immediately after use.

• Infectious samples such as prions and toxins are used within the laboratory. All such samples have associated COSHH procedures. If you are not sure what a sample is, treat it with caution. All samples which carry a hazard risk should be labeled as such.

• All waste solvent should be placed in the waste solvent bottle in the safety cabinet. Chemicals for removal should be referred to the Departmental Safety Officer.

• Sharps are collected in marked sharps bins and are then taken to a collecting point.

• The gas supply to the wet lab has been disconnected. Do not use naked flames in the lab as they are a severe risk, use a hotplate instead.

• The floors in the laboratory have been sealed to protect them from liquid nitrogen. Chairs with wheels must not be used on this surface as they are a potential slip hazard.

• The weekly laboratory rota maintains the liquid nitrogen tanks and checks cleanliness and safety. The tidier the laboratory is, the safer it is.

Liquid nitrogen

• Oxygen depletion is the main danger from the use of liquid nitrogen. Oxygen monitors have been installed in the laboratories and will issue an alarm if the oxygen levels in the room fall to dangerous levels. All new users must be shown the alarm system. Sometimes the refilling of dewars can cause the alarm to beep. If the alarm beeps, check the reading on the oxygen meter. If the reading is less than 19% leave the room. The alarm can be stopped with the red mute button but if the meter reads less that 19% or the alarm restarts, it is not safe to stay in the room and it must be evacuated. Once the room has been evacuated and the nitrogen has been allowed to disperse, the oxygen meter can be checked but by no less than two people. One person should hold their breath and check the meter reading while the other holds the door and watches the person checking the meter. The room can be used again once the reading has risen above 19%. The only button to be touched on the oxygen meter is the mute button; at no point should the settings on the meter be altered by anyone other than a service engineer or EM lab manager.

• Eye protection and gloves must be worn whenever handling cryogenic liquids.

• When handling liquid nitrogen remember to open any curtains and doors to avoid oxygen depletion.

• For more information the College's regulations on liquid nitrogen safety, click here.

Ethane

• The preparation of liquid ethane for cryo work must only be done behind the shield in the fume hood. Use low flow rates of ethane to prevent splashing.

• Gloves and eye protection must be worn.

• Ethane is flammable and potentially explosive. Do not use in the presence of flames and use only in a vented area. Once the ethane cylinder is open do not switch anything on or off in the fume hood, including the light. Do not create any static.

Laser

• You must wear the correct safety glasses when operating the laser.

• Make other people in the vicinity aware that you are using the laser.

• Do not look at the laser beam directly.

• Remove the key from the laser when leaving the room at any time. Do not leave the laser on and unattended.

Electron microscope emergency shut down

In the case of an emergency, such as a fire or a building evacuation, follow the instructions below. However, personal safety remains a priority at all times and by no means should you put yourself at risk.
 

• Press the OFF button on the Emergency Control Panel, which is on the right hand side of the EM column. The microscope will shut down and minimize any hazards to itself or anyone nearby.

• Switch off the PC by pressing the on/off button on the main PC box. Do not use the standard Windows shutdown procedure.

• Immediately leave the microscope room and follow the normal College evacuation procedures.

• If there is a risk of electrocution, the main power switches (grey boxes with levers) for each microscope are located near the exit doors of the microscope rooms.

Sulphur hexafluoride gas

The FEG microscope uses sulphur hexafluoride gas (SF₆) for insulation of the high tension (HT) tanks and the emission chamber of the F20. The gauge on the HT tank should read 4.5 bar. If the pressure drops below 4 bar, there may be a leak. While this gas is non-toxic it is heavier than air, and will displace oxygen from the floor level upwards. If there is a significant leak of this gas the oxygen monitor in the room will beep. The microscope will automatically switch off and the room should be evacuated according to the following procedure.

• If the microscope has not shutdown automatically, press the OFF button on the Emergency Control Panel on the right hand side of the EM column. Leave the room. Shut the door and put up a notice prohibiting others from entering.

• If a leak occurs during the daytime contact the EM Laboratory Manager, Dr Luchun Wang. If the leak occurs out of hours contact the Lab Manager as soon as possible so they can contact Phillips to notify them of the SF₆ leak.

• The College attendant on duty at the front desk  should be notified of the reason for the alarm (x6031). Access to the room must be prohibited until the gas has been cleared by the air circulation system (½ - 1 hr) and the oxygen levels have recovered to normal. To check that the gas has dispersed, follow the safety instructions on oxygen depletion found in the liquid nitrogen section.

• For routine venting of the SF₆ by the service engineer, the gas should be vented into one of the balloons stored for this purpose. The balloon can then be emptied outdoors in an open area.