Safe use of equipment in the lab
There are a number of pieces of equipment in the lab that require extra care in their use. It is essential that you have adequate training in the use of all equipment before attempting to use it. If you have not had training do not use any equipment until you have spoken to the technical staff.
If you have never used the centrifuges before, it is essential that you seek advice before attempting to use it. Misuse of the centrifuge can cause irreparable damage. There are various makes of centrifuge in the labs and all will have slightly different operating instructions. Do not assume that they are all set to do what you want them to do.
All centrifuges must be fitted with a locking device, which prevents the lid being opened whilst the rotor is in motion. It is foolish and dangerous to try to by-pass this lock. It is a contravention of the departmental safety policy and is therefore also illegal!
The rotor must be balanced before the centrifuge is switched on. This involves ensuring that the sample buckets positioned opposite each other on the rotor weigh the same. This is very important, as an imbalance will cause the rotor to wear and possibly crack. The centrifuges do have lights to indicate whether they are properly balanced, but these only come on once the speed of the rotor has reached 1000 rpm and this is often too late to prevent damage. A broken rotor travelling at high speed is capable of breaking through the outer casing of the centrifuge; accidents of this nature are potentially fatal.
Centrifuge tubes are designed to withstand certain spin speeds. Always make sure that the tubes are fit for the purpose that you are using them for. Never take a tube up to a speed higher than their specification states – this will break the tube and may damage the centrifuge and you will loose your sample! If your sample is not separating as you would like, you may have to spin it for longer instead of using a higher speed.
Should a tube break in the centrifuge, clean the centrifuge, including the sample buckets, immediately. This may prevent later breakages, which are often due to small fragments of glass or dust in the tube holders. If the spilt sample contains any hazardous substance please inform a member of technical staff so that they can advise on the best method for cleaning the centrifuge – do not leave broken tubes and spillages for someone else to find later.
Use of corrosive chemicals in the centrifuge;- Tubes should be stoppered if they contain corrosive chemicals. This will prevent any fumes corroding the inside of the casing. If the tube cannot be sealed – for example if gases are being evolved which would cause pressure to build in a sealed tube – then the centrifuge must be cleaned thoroughly as soon as the samples are taken out.
Cleaning the centrifuges – It is the responsibility of the lab user to clean the centrifuge after use. The buckets and holders must be washed thoroughly in soapy water and the inside of the centrifuge should be wiped out. Once the buckets and holders have been cleaned they should be left next to the centrifuge to ensure that they are perfectly dry before being replaced. This will also give the next user an indication that the centrifuge is clean and ready to use. Failure to do this could result in damage to the centrifuge.
17.2 Furnaces and ovens (B11)
There are 3 “muffle” furnaces in the lab. These are capable of heating to temperatures in excess of 1000 degrees Celsius. There are no interlock devices to prevent the furnaces from being opened when they are hot and quite often it is necessary to do so. This procedure should be carried out with great care - stand to one side of the furnace as the door is opened. It is essential to wear the protective gloves provided, as well as lab coat (with sleeves rolled down) and safety glasses. Tongs are provided for loading/unloading the furnace. Practice using the tongs before attempting to pick up a precious or extremely hot sample.
The furnaces may not be left on overnight.
There are also 2 drying ovens. The ovens are less hazardous, but care should still be taken when using them. If they are to be left on overnight, a notice must be left on them giving instructions of what to do in cases of emergency. Remember that although you may know what is in the oven overnight security staff/cleaners etc. do not.
Always check the temperature at which the ovens and furnaces are set. They are used at various settings and may not be set at the temperature you require.
An important point to remember:
HOT glass and porcelain look exactly like COLD glass and porcelain.
Do not test them with you fingers. Always wear the appropriate gloves when removing things from the ovens.
17.3 Microwave digestion system
If you intend to use the microwave digestion system you will need to book the prep room as well. Chemicals should be added to the vessels in the fume cupboard. Please avoid carrying the carousel around the labs when the vessels are full.
Always inspect the vessels for signs of damage before use. The microwave digestion system must only be used by trained and authorised persons.
The following is a list of general guidelines as laid down by the manufacturers:
- All vessel components must be dry and free of particulate matter. Drops of liquid or particles will absorb microwave energy, causing localised heating that may char and damage vessel components, leading to possible vessel failure.
- Never heat liquids in a sealed vessel or container that is not equipped with a pressure relief device.
- Never attempt to digest samples larger than 0.5 grammes if the organic content and composition of the sample is unknown.
- When working with an unknown sample, always perform a pre-digestion step in an unsealed, open vessel, allowing a minimum of 15 minutes for the reaction of volatile or easily oxidised compounds to subside before sealing the vessel and microwave heating.
- Micro wave heating of alkaline or salt solutions will concentrate these solutions, causing precipitation of salts and formation of crystal deposits on the vessel walls. These crystals will absorb microwave energy. This will cause localised heating that may char and damage the vessel components, leading to possible failure.
- Do not heat high boiling point acids (conc. sulphuric or phosphoric) inside the digestion vessel. The vessels cannot withstand the temperatures that these acids will reach and they will melt.
17.4 UV emitters
A UV light box is used in the lab to cure Norland slide mountant. The light must never be switched on if it is not mounted in the wooden box. Do not place hands inside the box when the source is on. Never leave the light on for longer than 15 minutes. Never look directly at the light source.
17.5 Sieve shakers
The sieve shaker for dry sieving is noisy and is housed in an acoustic box. Do not operate the shaker unless the door to the acoustic enclosure is shut.
When using the sieve shaker, ensure the sieves are properly stacked and the top is firmly clamped down. Always switch off at the plug before removing sieves.
A shaker is available for wet sieving. This should only be used with stainless steel sieves. As with the dry sieve shaker, ensure that the sieves are properly clamped down before switching on.
Do not operate the shakers without putting lids over the top sieve.
17.6 Freeze drier
A booking system is in operation for the use of the freeze drier. Please allow time for freezing samples before the date booked for using the equipment. It should be noted that the time taken for samples to dry will depend upon the number and size of samples placed in the chamber and upon the water content.
All users of the freeze drier are requested to complete the log book found adjacent to the freeze drier – worker using, sample description, date/time in, expected date time out.
The freeze drier may be used for drying samples that would degrade if dried at high temperature. There are various safety issues involved with its use and anyone wishing to use the freeze drier should read and sign the associated risk assessment first.
The following points should be noted:
- The freezer operates at a temperature of about –40oC and the base plate can cause burns if touched with bare skin.
- The plastic chamber is used under vacuum. It should be visually inspected before use and if there is any damage to it, it must not be used. Even the slightest flaw can cause the chamber to implode…
- Check the oil level in the vacuum pump before switching it on. Apart from damaging the pump, a lack of oil in the pump will cause it to overheat and could start a fire.
- The freezer chamber must be allowed to defrost between batches of samples. Ice will block the tubes and prevent the vacuum pump from working efficiently. This may cause the pump to over heat. It is not sufficient just to wait until the temperature indicator is at room temperature – this does not mean the ice has thawed. It will take several hours for all the ice to melt.