A bioclean room, or clean room, is any enclosed area where there is control over viable and nonviable particulates in the air with temperature, humidity, and pressure control as required to maintain specified standards. A viable particle is a particle that will reproduce to form observable colonies when placed on a specified culture medium and when incubated according to optimum environmental conditions for growth after collection. A nonviable particle will not reproduce to form observable colonies when placed on a specified culture medium and when incubated according to optimum environmental conditions for growth after collection.
Scientists and engineers operate a bioclean room with emphasis on minimizing airborne viable and nonviable particle generation or concentrations to specified levels. Particle size is expressed as the apparent maximum linear dimension or diameter of the particle—usually in micrometers (pm) or microns. (A micron is one-millionth of a meter.)
There are three clean-room classes that are based on total (viable and nonviable) particle count with the maximum number of particles per unit volume or horizontal surface area being specified for each class. The cleanest, or most stringent, airborne particulate environment is called a Class 100 Bioclean Room (or a Class 3.5 Room in SI units). In this type of bioclean room, the particle count may not exceed a total of 100 particles per cubic foot (3.5 particles per liter) of protecting any native life-forms on Mars, no matter how humble, from contamination by terrestrial microorganisms.
These new recommendations recognize the very low probability of growth of (terrestrial) microorganisms on the Martian surface. With this assumption in mind, the forward contamination protection policy shifts from probability of growth considerations to a more direct and determinable assessment of the number of microorganisms with any landing event. For landers that do not have life-detection instrumentation, the level of biological cleanliness required is that of the Viking Project spacecraft prior to heat sterilization. Class 100,000 clean-room assembly and component testing can accomplish this level of biological cleanliness. This is considered a very conservative approach that minimizes the chance of compromising future exploration. Landers with life-detection instruments would be required to meet Viking Project spacecraft poststerilization levels of biological cleanliness or levels driven by the search-for-life experiment itself. Scientists recognize that the sensitivity of a life-detection instrument may impose the more severe biological cleanliness constraint on a Mars lander mission.
Included in recent changes to COSPAR's planetary protection policy is the option that an orbiter spacecraft not be required to remain in orbit around Mars for an extended time if it can meet the biological cleanliness standards of a lander without life-detection experiments. In addition, the a size 0.5 micrometer (pm) and larger; the viable particle count may not exceed 0.1 per cubic foot (0.0035 per liter) with an average value not to exceed 1,200 per square foot (12,900 per square meter) per week on horizontal surfaces. A Class 10,000 Bioclean Room (or a Class 350 Room in SI units) is the next-cleanest environment, followed by a Class 100,000 Bioclean Room (or a Class 3,500 Room in SI units).
In aerospace applications, bioclean rooms are used to manufacture, assemble, test, disassemble, and repair delicate spacecraft sensor systems, electronic components, and certain mechanical subsystems. Aerospace workers wear special protective clothing, including gloves, smocks (frequently called bunny suits), and head and foot coverings to reduce the level of dust and contamination in clean rooms. A Class 10,000 Bio clean Room facility is typically the cleanliness level encountered in the assembly and testing of large spacecraft. If a planetary probe is being prepared for a trip to a possible life-bearing planet such as Mars, care is also taken in the bioclean room to ensure that "hitchhiking terrestrial microorganisms" are brought to the minimum population levels consistent with planetary quarantine protocols—thereby avoiding the potential of forward contamination of the target alien world.
Planetary scientists and exobiologists will place extraterrestrial soil and rock samples that are possibly life-bearing in highly isolated and highly secure bioclean rooms. This will help to avoid any possible back contamination of the terrestrial biosphere as a result of space exploration missions involving sample returns from alien worlds.
probability of inadvertent early entry (into the Martian atmosphere) has been relaxed compared to previous requirements.
The present policy for samples returned to Earth remains directed toward containing potentially hazardous Martian material. Concerns still include a difficult-to-control pathogen that is capable of directly infecting human hosts (currently considered extremely unlikely) or a life-form that is capable of upsetting the current ecosystem. Therefore, for a future Mars Sample Return Mission (as discussed in chapter 4), the following backward contamination policy now applies. All samples would be enclosed in a hermetically sealed container. The contact chain between the return space vehicle and the surface of Mars must be broken to prevent the transfer of potentially contaminated surface material by means of the return spacecraft's exterior. The sample would be subjected to a comprehensive quarantine protocol to investigate whether or not harmful constituents are present. It should also be recognized that even if the sample return mission has no specific exobiological goals, the mission would still be required to meet the planetary protection sample return procedures as well as the life-detection protocols for forward contamination protection. This policy not only mitigates concern of potential contamination (forward or back), but it also prevents a hardy terrestrial microorganism "hitchhiker" from masquerading as a Martian life-form.
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