November 1994

Effective Sterilization: The Autoclave

The autoclave is the best known and most common piece of sterilization equipment used in hospital and clinical research laboratories. It sterilizes items placed within its chamber by displacing air with steam and exposing them to great heat over a defined period of time. There are many variables that contribute to effective steam sterilization, so make sure that the autoclave functions optimally and that it is properly loaded in order to reduce any chance of ineffective sterilization.

How The Autoclave Works

There are two general types of steam sterilizers: gravity displacement, in which the displaced air flows out the drain through a steam-activated exhaust valve; and pre-vacuum, in which a vacuum is pulled to remove the air before steam is introduced into the chamber. With both types, as the air is replaced with pressurized steam, the temperature in the chamber increases. This results in temperature increases within the load that, under most conditions, are sufficient to treat the materials to be sterilized.

Treatment by steam sterilization is time and temperature dependent; therefore, it is essential that the entire load be exposed to the necessary temperature for a defined period of time. The autoclave's chamber usually heats up before the containers and the materials within it, so be sure to allow ample time for sterilization to occur. To kill most pathogens, a steam treatment takes about 30 minutes at 20 lbs./square inch. Some spore forming bacteria require a longer time for destruction.

Problems That Can Arise

For effective and efficient sterilization, degree of steam penetration is the critical factor. For steam to penetrate throughout the load, the air must be completely displaced from the treatment chamber. Residual air in the sterilizer chamber can prevent effective sterilization by:

  • reducing the ultimate possible temperature of the steam regardless of pressure
  • causing variations in temperature
  • prolonging the time needed to attain the maximum temperature
  • inhibiting steam penetration into porous materials

Loading The Chamber

Since sterilizer performance is directly related to this vital function of air displacement, ensure that the proper packaging materials are used and that the autoclave's chamber is properly loaded. To ensure that complete displacement of air will occur:

  • do not use deep containers (which may prevent displacement of air from the bottom)
  • do not use cardboard boxes or heat-sensitive plastic bags (which disintegrate during treatment and do not allow sterilization to occur). Use instead glass bottles or containers and plastic bags with temperature sensitive indicators that verify when the proper temperature has been achieved.
  • load the chamber properly (so steam can circulate freely within the chamber)
  • open all bags and loosen bottle caps and stoppers immediately before placement in the steam sterilizer
  • place plastic bags within a rigid container before steam treatment in order to prevent spillage and drain clogging

Other Tips

Never autoclave volatile chemicals, especially those having toxic vapors. Persons involved in steam sterilization should be trained in the proper techniques both to attain proper sterilization and to minimize personal exposure to the hazards posed by the wastes. These techniques include use of protective equipment, minimization of aerosol formation, and prevention of spillage during autoclave loading.

All steam sterilizers should be routinely inspected and serviced. Monitoring the steam sterilization process is required to ensure effective treatment. It is recommended that the sterilization process be monitored weekly to insure that proper procedures are being followed and that the equipment is functioning properly.

Bloodborne Pathogen Retraining: A New Format

The Department of Occupational and Environmental Safety has acquired several copies of the Bloodborne Pathogen Standard re-training videotape. Departments whose employees require annual bloodborne pathogen retraining can meet this requirement by showing the videotape at departmental meetings.

In addition to viewing the tape the following requirements must be met:

  • the attendance log enclosed with the copy of the videotape must be maintained and submitted to DOES after the session is complete. The attendance log must have: the instructor of the session (print and sign your name), the department, and the training session date and location. Each employee must then print and sign his or her name and social security number. It is vital that this log be kept and submitted to us.
  • OSHA requires that personnel have the opportunity to ask questions. Encourage your staff to call our department (x2907) or University Health Service (x2450) with any questions they may have.
  • If they have not already been vaccinated, each employee must be offered the opportunity to get vaccinated or sign a disclaimer declaring that they do not wish to be vaccinated at that time. This must be done at the retraining session.

Instructions for requesting a videotape are as follows:

  • call x2907 to reserve a copy of the tape. You will receive an attendance log and an instruction sheet along with the video.
  • Videotapes must be signed out and signed in upon its return.
  • Tapes will be lent out for three working days at a time. They must be returned by the assigned due date along with the completed attendance log.

Training on the dangers of occupational exposure to human blood and blood products is required at the time of initial assignment to tasks where occupational exposure may take place and annually thereafter as long as human blood or blood products are used.

DOES will still do the initial training when new employees are hired or newly assigned work with human blood products. However, the annual retraining session can be done much more conveniently by each department through use of this videotape.

If you have questions concerning running a retraining session, call DOES at x2907.

Industrial Hygiene on Campus

Industrial hygiene is a diverse field utilizing principles from chemistry, biology, and physics. Since its inception as a profession, industrial hygienists have been devoted to protecting the health of the worker and maintaining a safe workplace.

Industrial hygiene involves: preventing chemical exposure, determining if a worker has been exposed, and selecting the proper personal protective equipment to prevent future exposures. It also deals directly with the worker if there has been exposure to prevent it in the future.

The scope of an industrial hygiene project can range from checking the humidity level in a room to a large-scale environmental remediation project, such as what needed to be done in the Rockefeller building. DOES has also handled projects such as checking CWRU's drinking water for lead (there was none) and monitoring formaldehyde.

DOES has the capability to test for just about anything-if we cannot do it in house then we take the necessary sample and send it out for testing. Some of the more popular in-house testing we do checks for mercury, asbestos, formaldehyde, and organic solvents.

Preventing exposure and developing a safe environment are the most important aspect of industrial hygiene. Therefore the main tools of an industrial hygienist are preventative measures: proper training, the Chemical Hygiene Plan (CHP), and each chemical's Material Safety Data Sheets (MSDS), which provide a wealth of information about chemical use. Testing is always secondary to prevention.

If you believe you have an industrial hygiene problem, call Safety Services at x2907.

Containing Radioactive Liquid Waste

In order to make handling of liquid waste as safe as possible, researchers need to keep the following in mind:

  1. Store liquid waste in plastic, not glass bottles. This may prevent breaking or cracking.
  2. Double-contain it by placing it inside a deep tray or putting the bottle inside a bigger large-mouthed container. If the container should leak, there is a second one there to prevent the waste from spreading.

These items must be done before waste technicians will remove your waste. Reusable plastic containers can be ordered from scientific companies in various sizes-choose sizes that are easy to handle and that are appropriate to the amount of waste your lab produces. We recommend one-gallon containers unless your lab produces a large amount of short-term waste; then we can supply five-gallon containers.

Safety Manuals On-line

Both the Radiation Safety Manual and the CWRU Chemical Safety Manual are on-line and can be reached by any computer connected to CWRUnet.

To access these manuals on the Macintosh, go into "Administration zone" on CWRUnet, where you will see listed "Rad and Chem Safety." Follow the directory from there. The manuals are available in Microsoft Word, WordPerfect, and a standard RTF format to accommodate most word processors.

To access the manuals through DOS, you must use ftp. From CWRUnet, access the ftp program; from freenet type "go netapps" at the choice prompt. At the parameter (CWRUnet) or hostname (freenet) prompt, type in our number address "" At the Login (CWRUnet) or name (freenet) prompt, type in "ftp" or "anonymous." The subdirectories RadManual and ChemManual are in the SafetyDocs directory. CWRUnet will download files directly to your PC, while freenet will copy files to your work directory.

It is mandatory under OSHA that every lab have a copy of their Chemical Hygiene Program (most people have adopted the CWRU Safety Manual) readily accessible to every employee of that lab. It does not matter if the manual is on computer or in a hard copy, as long as every employee of the lab knows how to reach it quickly. However, the on-line versions of these manuals do not have the tables and charts appearing in the hard copy, so we recommend a hard copy of the necessary manual for every lab.

If you have any trouble accessing these manuals through CWRUnet, call DOES at x2906.

Distillation and Reclamation: CWRU's New Still

A spinning band still, designed to reclaim substances that would normally be disposed of as hazardous waste, is now in operation in Quail Building, next to the offices of the Department of Occupational and Environmental Safety.

The still is unique for several reasons, most importantly its size: it is capable of holding up to 50 liters at a time. It is equipped with a self-contained suppression system in case of fire, dyking, and it has a hydrocarbon alarm if temperatures increase so rapidly as to bypass the condenser.

Also unique is the still's computer system, which can be programmed to meet various specific needs. The still will heat at various step rates, depending upon the compound in the still and what safe distillation temperature is required. It can also be programmed to hold at specific condenser head temperatures in order to get the most precise cut possible, the purest distillation of the reclaimed substance.

The still's first project is "recycling" the chemical waste in Smith Building. Most of the hazardous waste that comes out of Smith consists of about 3% methyl isobutyl ketone (or MIBK, a regulated substance), 10% acetic acid, and water. The new still can reclaim the MIBK out of the waste at a 94% purity level, which can then be re-used by researchers. The remaining water and acetic acid solution, pH corrected to 7.0 to comply with sewer regulations, is no longer considered hazardous and can be poured down the drain.

This is only the first of many uses DOES has in mind for the new still: it will also be used to separate acetone, a regulated substance, out of the acetone and water solution used by many departments for rinsing glassware.

The savings to the university in the long run will be tremendous; for example, on the Smith Building project alone we will save $21,600 in disposal costs. This in itself nearly pays for the still (bought from BR Instruments at $24,000).

Just as important is the reduced amount of hazardous substances that the university will put into circulation: because substances like MIBK and acetone can be recycled and reused, it means less regulated substances must be bought and used on campus. This in turn drastically reduces the amount of hazardous waste that must be disposed of by the university, which not only saves the university money but reaffirms its commitment to be environmentally aware.

Any questions concerning the still and its uses for the future should be directed to the Safety Services division of the Department of Occupational and Environmental Safety at x2907.

Do You Have a Use for the Still?

The Department of Occupational and Environmental Safety is actively looking for more uses for the new still. If you think you have a substance that can be reclaimed, we would like to know.

Currently we are looking for Primary Investigators whose labs have a relatively pure waste stream containing common solvents such as xylene, tylene, or ethyl acetate. We can distill out of the waste a near chromatographically pure material, which we will return to the lab so it can be re-used. This way labs can save money, and more importantly, reduce the amount of waste being introduced into the environment.

Recycling is a smart move: we urge you to find out more about its uses and possibilities. If you think your lab has a use for the new still, or if you have questions about the possibility of recycling a part of your lab's waste, we encourage you to contact Richard Dell in the Safety Services department at x2907.