Laboratory Equipment, Part 4

Laboratory incubators come in various sizes and levels of technology.

All are designed to maintain set temperatures and conditions within the chambers. Some may have internal AC outlets so other devices can be used inside of the incubator. Be sure to inspect these outlets during your PM/inspection process for cracks and good ground contacts. Most will have fans to move heated air around the cultures, (specimens) and out a vent, although much of the air is recirculated. The doors must seal tightly and should only be opened on a strict as-needed basis. Every time the door is opened, it will take several minutes for the temperature and humidity to stabilize. A difference of 1°C can cause culture growth to slow or stop, which affects the clinical results.

All modern units will have digital temperature indicators and many will also have digital indicators for the levels of humidity and CO2. The technologist, the person using this equipment, should confirm any adjustments. Also, the inside of the incubator should be cultured and cleaned on a regular basis—usually monthly—by the technologist. If there are questions on the CO2 levels, the biomed may be asked to perform the checks. This has traditionally been done using a device called a Fryrite, but it can also be done more quickly using a CO2 level monitor borrowed from the anesthesia department. This can cut the time to make the CO2 adjustment from several hours to minutes.

There generally is at least one light in the incubator, not only for visibility but to promote the growth in the cultures. If the light needs to be replaced, you must use an exact replacement, not just one that fits. The emitted light spectrum is very important for the proper functioning of the incubator.

Filters on the air system must be cleaned on a regular basis. In most cases, the technologist will do the replacement or cleaning during the normal cleaning of the incubator. It is not a good idea to remove and clean the filter while cultures are in the incubator. Also, any moisture traps should be cleaned at the same time.

Common problems
    •    door gaskets leaking
    •    fan not working
    •    CO2 level out of specification
    •    uneven heating, generally caused by fan failure or blockage

Laboratory Ovens
Laboratory ovens are used to dry samples and for evaporating, dehydrating, or sterilizing. On a limited basis, some are used as a dry incubator. The simplest ovens are little more than a chamber heated by a resistance coil with a light to indicate that it is heating and a control for the temperature. Temperature is measured with a simple thermometer with its bulb in the chamber and its scale sticking out of the top of the unit. Some units also have a built-in fan to move the air from the coils into the chamber.

Common problems
    •    burned out light/lamp
    •    door gaskets
    •    fan not working
    •    broken thermometer

The more advanced ovens will have double doors, temperature recorders, and digitally selected temperatures. Their temperature regulation is much better than the simple ovens, and they are sometimes used as a dry incubator for culture preparation. The common problems are the same as with the simple ovens.

Measuring leakage currents on these devices will indicate the condition of the heating elements. As the elements age, their leakage increases; and when they reach the top limit of the allowed current limits, you can expect a failure on the next inspection.

Benchtop Devices
In all laboratories you will encounter numerous small devices that will require inspection and testing. Some devices, such as Bunsen burners, only need the hose to be inspected for leaks; and if there are leaks, you will generally smell the gas long before you can see the cracks in the hose. Closely follow the hospital’s policies and procedures if you suspect that there is a gas leak from a source other than the hose.

Such devices as immersion and mantle heaters either work or not. Unless there is a problem with the power cord or connector, these are not generally repairable items. As with any heater, electrical safety testing needs to be done and when leakage readings get close to the top of the acceptable range, they should be scheduled for replacement. There is a combination immersion heater/circulating pump that can be used to turn any watertight vessel into a circulating water bath. The temperature control is not precise but it is in general use where temperature control is not critical.

There are numerous types of baths/heating blocks used in the laboratory area. The simplest units have a heater pad bonded to the underside of the bath. The pad conducts heat through thermally conductive beads to test tubes or flasks placed in the baths, called dry baths or bead baths. Another version of this has metal blocks drilled with holes that fit test tubes.

A blood-bank water bath is a circulating water bath with an associated temperature control and low-water alarm circuits. This type of a bath is used specifically in the blood bank to thaw out frozen blood products before distribution to the clinical users.

Another version of the bath is filled with water, and flasks are placed in the water for heating. A variation of this is the shaking water bath. This consists of a rack that is about half the size of the bath that is suspended in the water and moved laterally via a motor-driven cam. The rack glides on nonstick bearings or rollers. The speed of the rack is adjustable via a motor control. In another version of this bath, a heating rod, instead of the contact heaters, is used.

A floatation bath is used in histology and is often confused with a water bath. There are several major differences between them. Most noticeable is that the floatation bath has a removable glass liner and is only about 2.5 cm deep. In most cases, there also is a light that illuminates the bath so the floating specimen section can be easily picked up with a glass slide being passed under it.

Hot plates and hot-plate stirrers are very common in laboratories. These are simple units with contact heaters under the surface on which flasks are placed. The heater regulation is ±2°C, and their use is limited by their capacity to heat large volumes of material. The stirrer version has a small variable-speed motor under the heater with a permanent magnet mounted on the shaft. A stir bar is placed in the flask sitting on the heater and as the motor/magnet rotate so does the stir bar, creating a vortex mixing of the fluids. The stir bar can be magnetic or made from material that responds to magnets. It must be coated with a material that will not react with the solutions being stirred. Always inspect any heater element for cracking and signs of damage and replace as needed.

Another benchtop stirrer is called a vortex genie. This is a cube-shaped device with a rubber cup on the top. When a test tube is held on the rubber top it energizes a motor in the cube that shakes the rubber cup in such a manner that it creates a vortex effect in the fluid thereby mixing it. This is only used for single test tubes.

Many of these devices have minimal thermal protection systems in them. Overheating can be a problem, and, during PM/inspection cycles, you should look for signs of heat damage to the devices.

The Bacti incinerator is found in various parts of the clinical laboratory and is a simple device. It consists of a resistance coil heater with a small opening in the center into which small samples are inserted, generally on the tip of a ceramic spatula. This dehydrates the specimen as part of the preparation for examination under a microscope. There are no controls for heat level, only an on/off switch. Because heat is generated by this device, the protective shield should be examined to be sure that it is secure and fully protects the user.

Mixers/homogenizes are also known widely as blenders. They are available both in handheld and counter versions, as are those in your kitchen. Many are two-wire devices.

The last of the minor bench devices are the tube rockers and rotators. A tube rocker is a device that slowly moves small test tubes, 20 cc and under, over a 45° arc. It has a small clock motor that is connected to a cam that moves the back and forth through the arc. This is often a two-wire, double-insulated device. A tube rotator handles larger test tubes; it is also run with a clock motor that is directly coupled to the disc that holds the test tubes. Both of these devices are generally a single speed and not used for long periods of time.

Common problems, all devices
    •    spills, leaks
    •    heater failures or high electrical leakage
    •    missing hardware, loose or worn mechanical linkages
    •    temperature control

When working on laboratory devices it is very important to communicate with the person who operates the device and follow all the rules of the lab. This may include having to gown up, preclean test equipment and tools before entering the area, and postclean it upon leaving. At minimum, always wear gloves when working on any device that has been in contact with body fluids, even if it has been cleaned. Along with all the normal chemical and biological hazards associated with a lab, you can run into radioactive material and some very toxic agents when in research areas.

David Harrington, PhD, is director of staff development and training at Technology in Medicine, Holliston, Mass.

Contributing to this article was Edwin Bellamy, II, CBET, the Technology in Medicine account manager at Quincy Medical Center, Quincy, Mass.