Clemson University

2. Safe Work Practices with Laboratory Equipment

a.     Equipment maintenance:  Good equipment maintenance is important for safe, efficient operations. Equipment should be inspected and maintained regularly. Servicing schedules will depend on both the possibilities and the consequences of failure. Maintenance plans should include a procedure to ensure that a device that is out of service cannot be restarted.

b.     Guarding:  All mechanical equipment should be adequately furnished with guards that prevent access to electrical connections or moving parts (such as the belts and pulleys of a vacuum pump). Each laboratory worker should inspect equipment before using it to ensure that the guards are in place and functioning.

c.     Shielding:  Safety shielding should be used for any operation having the potential for explosion/implosion such as (a) glassware under pressure (b) whenever a reaction is attempted for the first time (small quantities of reactants should be used to minimize hazards); (c) whenever a familiar reaction is carried out on a larger than usual scale; (d) whenever operations are carried out under non-ambient conditions. Shields must be placed so that all personnel in the area are protected from the hazard. 

d.     Glassware: Accidents involving glassware are a leading cause of laboratory injuries.

  • Borosilicate glassware is recommended for all laboratory glassware except for special experiments that use UV or other light sources.
  • Careful handling and storage procedures should be used to avoid damaging glassware. Damaged items should be discarded or repaired.
  • Adequate hand protection should be used when inserting glass tubing into rubber stoppers or corks or when placing rubber tubing on glass hose connections. Tubing should be fire polished or rounded and lubricated, and hands should be held close together to limit movement of glass should fracture occur. The use of plastic or metal connectors should be considered.
  • Glass-blowing operations should not be attempted unless proper annealing facilities are available and properly trained personnel are conducting the operation
  • Vacuum jacketed glass apparatus should be handled with extreme care to prevent implosions. Equipment such as Dewar flasks should be taped or shielded. Only glassware designed for vacuum work should be used for that purpose.
  • Hand protection should be used when picking up broken glass.
  • Proper instruction should be provided in the use of glass equipment designed for specialized tasks, which can represent unusual risks for the first-time user. (For example, separatory funnels containing volatile solvents can develop considerable pressure during use.)

e.     Cold Traps and Cryogenic Hazards:  The primary hazard of cryogenic materials is their extreme coldness. These, and surfaces they cool, can cause severe burns if allowed to contact the skin. Gloves and a face shield should be used when preparing or using some cold baths. Neither liquid nitrogen nor liquid air should be used to cool a flammable mixture in the presence of air because oxygen can condense from the air, which can cause an explosion hazard. Cryogenic or loose, dry leather gloves must be used when handling dry ice, which should be added slowly to the liquid portion of the cooling bath to avoid foaming over. Workers should avoid lowering their head into a dry ice chest (carbon dioxide is heavier than air, and suffocation can result).

f.      Systems Under Pressure: Reactions should never be carried out in, nor heat applied to, an apparatus that is a closed system unless it is designed and tested to withstand pressure. Pressurized apparatus should have an appropriate relief device. If the reaction cannot be opened directly into the air, an inert gas purge and bubbler system should be used to avoid pressure buildup. Appropriate shielding must be provided whenever chemicals are heated or reactions are carried out in systems under pressure.

g.     Extractions and Distillations


      Extractions can present a hazard because of the potential buildup of pressure from a volatile solvent and an immiscible aqueous phase. Glass separatory funnels used in laboratory operations are particularly susceptible to problems because their stoppers or stopcocks can be forced out, resulting in a spill of the contained liquid. It is even possible for pressure to burst the vessel.

       To use a separatory funnel correctly, do not attempt to extract a solution until it is cooler than the boiling point of the extractant. When a volatile solvent is used, the unstoppered separatory funnel should first be swirled to allow some solvent to vaporize and expel some air. Close the funnel and invert it with the stopper held in place and immediately open the stopcock to release more air plus vapor. Do this with the hand extended around the barrel to keep the stopcock plug securely seated.

       Point the barrel of the separatory funnel away from yourself and others and vent it to the hood. Do not vent the funnel near a flame or other ignition source. Close the stopcock, shake with a swirl, and immediately open the stopcock with the funnel in the inverted position to vent the vapors again. If it is necessary to use a separatory funnel larger than one liter for an extraction with a volatile solvent, the force on the stopper may be too great, causing the stopper to be expelled. Consider performing the extraction in several smaller batches.


       Potential dangers arise from pressure buildup, commonly used flammable materials, and the use of heat to vaporize the chemicals involved. Careful design and construction of the distillations system is required to accomplish effective separation and avoid leaks that can lead to fires or contamination of the work area.

       It is necessary to ensure smooth boiling during the separation process and avoid bumping, which can blow apart the distillation apparatus. Stirring the distillation mixture is the best method to avoid bumping. Boiling stones are only effective for distillations at atmospheric pressure. Use fresh boiling stones when a liquid is boiled without stirring. Do not add boiling stones or any other material to a liquid that is near its boiling point, because this may cause it to boil over spontaneously.

      An electric mantle heater, a ceramic cavity heater, steam coils, or a nonflammable liquid bath are the best to provide even heating. Silicone oil or another suitable high-boiling-temperature oil can be used on a hot plate. Hot water or steam may also be used in some cases. An extra thermometer inserted at the center bottom of the distilling flask will warn of dangerously high temperatures that could indicate exothermic decomposition. Do not distill or evaporate organic compounds to dryness unless they are known to be free of peroxides.

       Because superheating and bumping occur frequently during distillation using reduced pressure, it is important that the distillation assembly is secure and the heat distributed more evenly than is possible with a flame. Evacuate the assembly gradually to minimize the possibility of bumping. Stirring, or using an air or nitrogen bleed tube, provides good vaporization without overheating and decomposition.

      Put a standing shield in place for protection in the event of implosion. After finishing a reduced-pressure distillation, cool the system, and then slowly bleed in air so as not to induce an explosion in a hot system. Pure nitrogen is preferred to air and can be used even before cooling the system. Use a face shield when working directly with a distillation unit.

       In a steam distillation, minimize the accumulation of condensate in the distillation flask. The heat of steam condensation is very high, and overfilling the flask is less likely if condensation from the entering steam line is trapped and the flask heated or insulated to prevent excessive condensation.

Handling and Care of Apparatus with Glass Joints: 

All glass joints should be kept completely free from dirt. Dust in a glass joint may cause leakage and grit may even cause breakage. Therefore, before use, glass joints should be wiped free from foreign matter. After use, joints should be separated as soon as possible, preferably while still warm to prevent seizure.

Seizure of Glass Joints

Seizure of Quickfit ground conical joints may be due to cementation. Sodium hydroxide should never be allowed to remain in contact with the ground joint surface. It attacks the matt surface very rapidly and the products of the attack, if left between two ground surfaces, will cement together. Jamming may also cause seizure. Although Clearfit glass joints are less prone to seizure, it is necessary to exercise similar precautions when handling them.


For work under atmospheric pressure, lubricant is normally not required. Lubrication of the ground joints with grease is essential, however, when conducting distillation under reduced pressure or when there is possibility of basic solution coming into contact with the ground glass surface. Petroleum jelly or silicone stopcock grease can normally be applied, but silicone high vacuum grease is necessary for best result. Excess grease will contaminate reaction products and such must be avoided. When using a silicone grease, care should be taken to ensure that jointed equipment is not left assembled for any length of time as “dry out” of the lubricant may occur causing seizure of the joints.

Clamping of glassware

Supporting rather than clamping forcefully should always be the first principle in assembling glassware. Clamps should only be tightened to fingertip-tightness (i.e., not too tight). Before tightening the clamps to the stand, it must first be ascertained that the apparatus is free from physical strain.

Cleaning and Care of Glassware

Clean apparatus is essential for laboratory work. If grease is used to lubricate the glass joints, the joints should first be carefully wiped clean with tissue paper, and the remaining grease then removed with cotton and wool containing ether or chloroform. After that, the glassware should be washed properly with detergent. If washing up is done immediately after an experiment, it is nearly always possible to remove organic compounds from glass apparatus. If a brush is used inside the flask, avoid scratching the glass with the metal parts. Glass apparatus is best left to drain dry in a rack or it may be dried in an oven.

Care should be taken to avoid scratches on the surface of glassware as these will reduce the mechanical strength of the glass and make it more susceptible to breakage through thermal shock. Proper cleaning and storage of flasks will lengthen their life significantly. Scratches sufficient to cause breakage are produced often by unprotected glass stirrers, rubbing or knocking two flasks together, or by the metal stems of cleaning brushes.

h.    Electrical Equipment:  Electrical currents of very low amperage and voltage may result in fatal shock under certain circumstances. Voltages as low as 24 volts AC can be dangerous and present a lethal threat. Low-voltage DC currents do not normally present a hazard to human life, although severe burns are possible. The duration of contact with a live circuit affects the degree of damage, especially with regard to burns.

  • All electrical switches shall be labeled, including circuit breakers in the service panels, and all laboratory personnel shall know where these controls are and how to shut off circuits or equipment in case of fire or other accident. Any electrical equipment that is not operating properly or seems to be overheating shall be turned off immediately and inspected by a qualified person.
  • Electrical equipment should be inspected periodically to confirm that the cords and plugs are safe condition. Circuit diagrams, operating instructions, descriptions of hazards, and safety devices are usually provided by the manufacturer and should be kept on file for reference.
  • Only three-wire grounded, double insulated or isolated wiring and equipment shall be used in 110V-115V AC applications. All wiring and equipment shall comply with the National Electrical Code. In specifically designated laboratories, cold rooms, or storage rooms or other locations where concentrations of flammable vapor-air mixtures are likely to occur, certified explosion-proof wiring and equipment, including light fixtures, switches, and refrigerators shall be used. If you have any questions with regard to the code, contact Environmental Safety (656-1806).
  • Series-wound motors with carbon brushes, typically found in household appliances such as blenders and mixers, are not spark-free and shall not be used in laboratories where flammable vapors accumulate. Equipment manufactured for use in laboratories generally contains induction motors.
  • Electrical extension cords should be avoided where practical by installing additional electrical outlets. When they are used, the wire gauge shall be equal to or larger than the size of the cord being plugged into them. Electrical cords on equipment shall be discarded or repaired if frayed or damaged. Cords should be kept as short as practical to avoid tripping hazards and tangles.
  • Place electrical equipment so as to minimize the possibility that water or chemicals could spill on it or that water could condense and enter the motor or controls. In particular, place such equipment away from safety showers. In cold rooms, minimize condensation by mounting electrical equipment on walls or vertical panels.
  • Electrical equipment shall be de-energized and tagged or locked out according to OSHA requirements before repairs are made. If adjustments or other contacts are to be made with energized electrical equipment, a second person shall be present. Be sure you are not on a damp surface or touching a potential grounding surface. Use insulated tools, keep your hands dry, and wear safety glasses to prevent injury from sparks.
  • If a worker receives an electrical shock and is in contact with the energized device, turn off the current if possible; or use non-conducting gloves or a non-conducting device to pull or push the victim free from the current source. Help victims only if you are certain that you will not endanger your own safety.

i.      Static Electricity is found wherever equipment is in operation, materials are processed, liquids are being poured, or personnel are moving about. Some common potential sources of electrostatic discharges are ungrounded metal tanks and containers; metal-based clamps, nipples, or wire used with non-conducting hoses; high-pressure gas cylinders upon discharge; and clothing or containers made of plastic or synthetic materials.

  • High voltages can be attained in a relatively short time span.
  • Hazard is greatest during wintertime when the air is dry, but often air conditioning can remove enough moisture for a hazard to exist during summer months.

       Many methods can be used to ground static electricity, but because of existing conditions in some areas the use of these grounding devices may be impossible to implement. Thus, personnel become the source of static charge. If personnel are engaged in work that could be hazardous because of accidental discharge of static electricity and cannot use grounding devices on their person, the simplest way to assure grounding is to make a contact with a water pipe. The static charge will transfer to ground via the pipe.

      Some commercially available devices for eliminating static electricity follow:

  • Humidifiers
  • Grounding straps: conductive strips or straps connected to machine belts, pulleys, and containers connected to the ground.
  • Conductive materials: conductive floor mats, bags, hose containers and container covers connected to the ground.
  • Personnel protection: shoe straps, wrist straps, aprons, gloves, and clothes, conductive items used in conjunction with other devices to assure grounding of personnel.

j.      Centrifuges: If a tabletop centrifuge is used, make certain that it is secured in a location where its vibration will not cause bottles or equipment to fall. Centrifuge rotors shall be balanced each time they are used. Securely anchor and shield each unit against flying rotors. Regularly clean rotors and buckets with noncorrosive cleaning solutions.

  • Always close the centrifuge lid during operation, and do not leave the centrifuge until full operating speed is attained and the machine appears to be running safely without vibration. Stop the centrifuge immediately and check the load balances if vibration occurs. Check swing-out buckets for clearance and support.

k.    Vacuum Pumps: If vacuum pumps are used with volatile substances, the input line to the pump should be fitted with a cold trap to minimize the amount of volatiles that enter the pump and dissolve in the pump oil.  The exhaust from evacuation of volatile, toxic, or corrosive materials shall be vented to an air exhaust system.

l.      Drying Ovens and Furnaces: Electrically heated ovens are commonly used in the laboratory to remove water or other solvents from chemical samples and to dry laboratory glassware before its use. With the exception of vacuum drying ovens, these ovens rarely have any provision for preventing the discharge of the substances volatilized in them into the laboratory atmosphere. Thus, it should be assumed that these substances will escape into the laboratory atmosphere and could also be present in concentrations sufficient to form explosive mixtures with the air inside the oven.

  • Ovens should not be used to dry any chemical sample that has even moderate volatility and might pose a hazard because of acute or chronic toxicity unless special precautions have been taken to ensure continuous venting of the atmosphere inside the oven. Thus, most organic compounds should not be dried in a conventional laboratory oven.
  • Glassware that has been rinsed with an organic solvent should not be dried in conventional ovens. If such rinsing is necessary, the item should be rinsed again with distilled water before being placed in the oven.
  • Because of the possible formation of explosive mixtures by volatile substances and the air inside an oven, laboratory ovens should be constructed so that their heating elements (which may become extremely hot and their temperature controls (which may produce sparks) are physically separated from their interior atmospheres. Small household ovens and other similar devices do not meet this requirement and, consequently, should not be used in laboratories. Existing ovens that do not meet these requirements should have a sign attached to the oven door to warn workers that flammable materials should not be placed in that oven.

                        Mercury thermometers should not be used in drying ovens.

m.   Refrigerators: The potential hazards posed by laboratory refrigerators are in many ways similar to those of laboratory drying ovens. Because there is almost never a satisfactory arrangement for continuously venting the interior atmosphere of a refrigerator, any vapors escaping from vessels placed in one will accumulate. Thus, the atmosphere in a refrigerator could contain an explosive mixture of air and the vapor of a flammable substance of a dangerously high concentration of the vapor of a toxic substance or both. (The problem of toxicity is aggravated by the practice of laboratory worker who place their faces inside the refrigerator while searching for a particular sample, thus ensuring the inhalation of some of the atmosphere from the refrigerator interior). The placement of highly toxic substances in a laboratory refrigerator should be avoided.

There are basically three types of refrigerators used in laboratories:

1. Household (Domestic): Refrigerators and freezers that can be used in laboratories for storage of aqueous solutions and nonflammable/non-explosive materials. 

2. Lab-Safe (Flammable Safe): Refrigerators and freezers which are used for

storage of flammable or explosive materials. This type of cooling technology has no internal switching devices that can arc or spark as a source of ignition. The compressor and other circuits usually are located at the top of the unit to reduce the potential for ignition of floor-level flammable vapors. These refrigerators also incorporate design features such as thresholds, self-closing doors, and magnetic door gaskets. Special

inner shell materials control or limit damage should an exothermic reaction occur within the storage compartment.

 3. Explosion-Proof: Refrigerators that are designed to be operational in areas where the air outside the refrigerator might be explosive. This often includes liquids, gases, or solids with flashpoints of less than 100F. Explosion-proof refrigerators feature enclosed motors to eliminate sparking and bear a FM® (Factory Mutual) or UL® (Underwriters Laboratory) explosion-proof label. This type of refrigerator requires direct wiring, is very expensive and is rarely necessary for use in university research laboratories.

Laboratory refrigerators should be placed against fire-resistant walls, have heavy-duty electrical cords, and preferably should be protected by their own circuit breaker.

Uncapped containers of chemicals should never be placed in a refrigerator. Containers of chemicals should be capped so as to achieve a seal that is both vapor tight and unlikely to permit a spill if the container is tipped over. Caps constructed from aluminum foil, corks, corks wrapped with aluminum foil, glass stoppers, or parafilm do not meet all of these criteria. The most satisfactory temporary seals are normally achieved by using containers that have screw-caps lined with either a conical polyethylene insert or a Teflon insert. The best containers for samples that are to be stored for longer periods of time are sealed, nitrogen-filled glass ampoules.

n.  Heating Devices: Perhaps the most common electrical equipment found in a laboratory are the devices used to supply the heat needed to effect a reaction or a separation. The use of steam-heated devices rather than electrically heated devices is generally preferred whenever temperatures of 100C or less are required; these devices do not present shock or spark hazards. Electrically heated devices include hot plates, heating mantles and tapes, air baths, hot-tube furnaces, and hot-air guns. They are inherently much safer than burners as laboratory heat sources; however, such devices can still pose both electrical and fire hazards if used improperly.

  • The actual heating element in any laboratory heating device should be enclosed in a glass, ceramic, or insulated metal case such that it is not possible for the laboratory worker (or some metallic conductor) to accidentally touch the wire carrying the electric current. This practice minimizes the hazards of electrical shock and of accidentally producing an electrical spark near a flammable liquid or vapor. This type of construction also diminishes the possibility that a flammable liquid or vapor will come in contact with the hot wire (whose temperature is frequently higher than the ignition temperature of many common solvents). If any heating device becomes so worn or damaged that its heating element is exposed, the device should either be discarded or repaired to correct the damage before it is again used in the laboratory.
  • The temperature of many laboratory heating devices (e.g., heating mantels, air baths, and oil baths) is controlled by use of a variable autotransformer that supplies some fraction of the total line voltage (typically 110V) to the heating element of the device. If a variable transformer is improperly wired, the switch on it may or may not disconnect both wires of the output from the 110V line when in the off position. If a grounded three-prong plug is not used, each output line may be at a relatively high voltage (e.g., 110 and 110V) with respect to an electrical ground. Because of these possibilities, whenever a variable transformer whose wiring is not definitely known to be acceptable is used, it is best to assume that either of the output lines could be at a potential of 110V and capable of delivering a lethal electric shock.
  • The cases of all variable autotransformers have numerous openings to allow for ventilation and some sparking may occur whenever the voltage adjustment knob is turned; laboratory workers should be careful to locate these devices where water and other chemicals cannot be spilled on them and where their movable contacts will not be exposed to flammable liquids or vapors. Specifically, variable autotransformers should be mounted on walls or vertical panels and outside of hoods; they should not be placed on laboratory bench tops, especially those inside of hoods.
  • Whenever an electrical heating device is to be left unattended for a significant period of time, it is advisable that it be equipped with a temperature-sensing device that will turn off the electric power if the temperature of the heating device exceeds some preset limit. Similar control devices are available that will turn off the electric power if the flow of cooling water through a condenser is unexpectedly stopped. Such fail-safe devices, which can either be purchased or constructed by a qualified technician, prevent more serious problems (fires or explosions) that may arise if the temperature of an unattended reaction should increase significantly either because of a change in line voltage or because of accidental loss of reaction solvent. These devices are also valuable accessories for use with stills employed to purify reaction solvents because such stills are often left unattended for significant periods of time.
  • Discard old hotplates and hotplates in disrepair. Hot plates purchased prior to 1984 do not have temperature feedback controls. These models include the Corning PC-35 and PC-351 and the Thermolyne Model:SP46925. Unplug inactive hotplates or heating mantles in close proximity to oil baths, combustible or flammables material. In the replacement and acquisition select hotplate housing designs, which are less affected by spills and aggressive environments. Where liquid spills can be anticipated (i.e. water cooled reflux) do not use hotplates that have open housing designs. Select hermetically sealed hotplate housing to protect the electronics from liquids and gases Additional hotplate safety features to look for are two independent temperature control circuits, which switch off heating in case of an over temperature situation. Alternatively, a hotplate can be powered up through a separate high temperature control unit. This approach physically separates the primary and high temperature sensor and related control /switch functions. Communicate to all lab personnel the critical importance of house keeping i.e. elimination of all combustible materials from the immediate vicinity (above, below, and on all sides) of the heat source. Do not heat flammable/combustible liquids on hotplates unless they are intrinsically safe (i.e., sealed). Post hotplates that are not intrinsically safe “Not for Use With Flammable liquids”. Consider the possibility the hotplate could spontaneously engage and heat up even when the switch is in the OFF position. Distribute “stir” and “heat” labels for older hotplates to reduce the possibility of user error. Where only stirring is required, acquire and use a stirrer instead of a hotplate/stirrer combination. Potential for liquid access through front cover and/or slots in housing.

o.  Assembling Apparatus: Operations that may generate airborne contaminants or that use flammable liquids or toxic, reactive, or odoriferous materials shall be conducted in a chemical hood or other appropriate containment enclosure. Whenever hazardous gases or fumes are likely to evolve, an appropriate trap, condenser, or scrubber shall be used to minimize release of material to the environment.

  • Apparatus should be set up well back from the edge of the work area. When assembled in a hood, apparatus should not obstruct the area. To avoid overflow, choose apparatus with at least 20 percent more capacity than would normally accommodate the volume of chemical planned for the operation. All parts of the apparatus shall be firmly balanced and supported. Tubing shall be fastened with wire or appropriate clamps.
  • Stirrer motors and vessels shall be positioned and secured to ensure proper alignment. Magnetic stirring is preferable, and non-sparking motors or air motors shall be used in any laboratory that might contain flammable vapors.
  • Funnels and other apparatus with stopcocks shall be firmly supported and oriented so that gravity will not loosen the stopcock plug. Use a retainer on the stopcock plug, and lubricate glass stopcocks. Do not lubricate Teflon stopcocks.
  • Include a vent in apparatus for chemicals that are to be heated, and place boiling stones in unstirred vessels. If a burner is to be used, distribute the heat with a ceramic-centered wire gauze. Insert a thermometer in heated liquids if dangerous exothermic decomposition is possible. This will provide a warning and may allow time to remove the heat and apply external cooling. A pan under a reaction vessel or container will confine spilled liquids in the event of glass breakage.
  • If a hot plate is used, be sure that its temperature is less than the auto ignition temperature of the chemicals likely to be released and that the temperature control device does not spark. Whenever possible, use controlled electrical heaters or steam in place of gas or alcohol burners.