I have read with great interest the story in the October issue, “Contamination found outside Class II BSC”. Please consider concerns I had with 2 statements made in this paper:
1. “They (procedures) produce spills inside the BSC, which then leak onto the floor and get traced around the pharmacy work areas.”
While I am not in a position to address the likelihood of a spill inside a Biological Safety Cabinet, the cabinets are specifically designed to prevent leakage of anything spilled inside. It does not seem possible that leakage onto the floor can happen in a cabinet designed to meet NSF International STD 49, the standard cabinets are manufactured to in the United States.
Spillage of aerosols out the front of the cabinet may be possible due to bad technique or improper certification. The statement, however, sounds as if liquid or powder is “spilling out the front of the cabinet.” It seems to me much more likely that any spillage in the work area would be onto the work tray of the front diffuser. The cabinets are designed to contain work area spills. In fact, cabinets are provided with a 4-liter spillage trough under the work surface to facilitate containment and decontamination of any spilled agents.
2. “They can also produce aerosols and vapors much smaller than 0.3 micron pore size of the BSC's HEPA filter, thus exposing the workers by inhalation when the vapors are released in to the environment.”
Unlike other types of filters, HEPA filters do not rely on “small pores” to trap particles. HEPA filter media is, in fact, a bed of glass fibers. HEPA filters are rated at 0.3 micron because that was originally thought to be the most penetrating particle size (MPPS). Current thought says the MPPS is between 0.1 and 0.25 micron depending on airflow and media grade. Particles larger than rated size are filtered by means of diffusion. The net result is that the filter rating represents roughly the efficiency of removal of the most difficult particles to trap. Both larger and smaller particles are actually removed more efficiently than the rated size. If your hazard is particulate in nature, there should be no significant penetration of those aerosols. If the hazard is a vapor it does not matter what size particle the filter is rated at, it will penetrate a mechanical filter.
There may be a concern regarding venting a BSC back into the pharmacy in certain cases, but these are design application issues and are in no way related to a “pore size.” The concern here is more a matter of proper hood selection to the hazard. If there is going to be a hazardous vapor generated, the correct cabinet choice would be a Class II Type B1, B2, or possibly even a B3, but never a Class II Type A vented back into the pharmacy.
Bad technique or improper cabinet selection may cause an exposure potential, as would misuse of any safety device. Clearly, the use of BSCs significantly impacted the safety of healthcare workers positively. While we agree that the identification of contaminants described in the article indicates that additional work needs to be done, encouraging distrust of one of the control measures that have definitively reduced their exposure is not helpful.
Why blame the operator?
I am writing to correct some misconceptions about the safe handling of potent materials stated in “Technique may be culprit behind Class II BSC contamination,” CleanRooms, November 1999, p. 1).
In the article, the blame for contamination of the environment is placed on the operators. It is certainly true that procedure can reduce the amount of powder liberated to the environment; however, it is impossible to expect perfect performance every time. Any system that does not allow for human error is the wrong system.
The culprit is the containment device, not the operator.
The manufacturers of safety cabinets have very little performance data other than simulated tests under ideal conditions. No allowance for system deterioration, utility malfunction and operator error is made in providing performance data, if any is available.
The people responsible for the safety of the operators normally have a very poor understanding of the safe levels for the materials being used, and probably infrequently monitor the performance in any meaningful way (such as using air samplers and chromatography.)
All toxic materials should have an Operator Exposure Level (OEL) designation. Where this is not available, a guide is that the operator should not be exposed to more than 1/1000 of a therapeutic dosage. Having discovered the OEL (for active cytotoxics this can be in the microgram to nanogram range), it is necessary to understand its meaning. A 1-microgram OEL equates to one or two grains of salt in a cubic meter of air over an 8-hour working day. Since Cytotoxic actives are generally micronized, the best way to demonstrate the effect is to crush one or two grains of salt and to blow them in the air. Try to find the salt!
Therefore, the “I can't see it so it cannot be there” school of thought does not apply.
The real problem highlighted by finding the active at all stages of operation is the way in which it is transferred in and out of the containment device and the method of decontamination of the device.
To really understand the problem, try taking some blue food color in powder form and attempt to pack it into the same packaging your active is in. There is absolute certainty that the active is on the outside of the packaging. Then take the material into the cabinet and dispense. When it passes out even more active is on the outside of the packaging. It is not possible to openly pass materials in and out without the risk of environmental contamination.
So any device with a pass in and pass out lock chamber is certain to be challenged. It is therefore essential to pass in only to such a chamber and to bag out in such a way that the outside of the bag out has never been contaminated.
A number of these systems are available. They work in much the same way as a sausage skin works. Heat sealing is imperative to ensure a seal and the bag out must be cut through the heat seal to avoid active liberation.
Alternatively, the pass out can be in a container with a containment port. Here the active must be separately contained from the port so that contamination of the seals on the port device is minimized
Wipe down decontamination is often used. In some cases the active can be de-activated readily. However, many of the compounds are not soluble and the wipe down will only distribute the active evenly.
The quickest route of ingesting active is by aspiration through the nose or mouth. Transdermal is a slower route but cannot be ignored. Mechanical transfer is a risk because the material escapes the containment boundary and is available for transdermal or aspirated transfer.
To be sure that no escape occurs, each case needs careful evaluation and assessment by an expert in the area of containment. At present, few such experts are available. Relying on the vendors is also a risk because the data they have is not always accurate. In a recent case I challenged a reputable major equipment manufacturer over the term “dust free” in his literature. He insisted that it meant exactly what it said. Later it was determined that a suitable OEL for this system was 30 micrograms not exactly dust free.
A further contribution to operator error is the failure to establish practical operating procedures and to use procedures that are ergonomically challenged. If the operator is concentrating on how to overcome ergonomic problems, accidents are inevitable. The procedures and their ergonomic challenges need careful review before blaming the operator.
So don't blame the operator if you have not provided:
- An ergonomically practical system
- A transfer system that works
- A containment system (isolator or safety cabinet that works)
- Workable SOPs
Julian Wilkins, principal consultant
PharmaConsult Us LLC