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Flow
Cytometry - More details about aerosols
(Author: P. Herman) (Last revised:
July 10, 2006
)
The larger particles of an aerosol drop to the floor (or to the bench), within seconds, where they form an agregate of dust that is unlikely dispersed into the air. Droplets larger than 140 micrometers tend to fall to the ground before they evaporate and those smaller than 140 micrometers would be more likely to evaporate before contacting the ground or any solid surface. Table 1 summarizes the evaporation times and falling distance of droplets based on size.
Table 1 : Evaporation times and falling distance of droplets based on size
| Diameter of droplets (micrometer) | Evaporation time (s) | Distance fallen before evaporation (meter) |
|---|---|---|
| 200 | 5.2 |
7.2 |
| 100 | 1.3 |
0.45 |
| 50 | 0.31 |
0.03 |
| 25 | 0.08 |
0.002 |
(adapted from Fleming D.O et al., Laboratory Safety, principle and practices, Second edition. 1995)
The particles coming from evaporated droplets are able to remain in the air for very long period. These tiny particles are called "droplet nuclei". If droplet nuclei contain an infectious agent (e.g M. tuberculosis) airborne transmission to human or animal is possible. If the micro-organisms (pathogen and/or genetically modified) are contained not in aquous but proteinaceaous fluids (sputum, mucus, serum) evaporation will be much slower as these material tend to retain water. The droplets will settle more rapidly; fewer will remain suspended in air and fewer infected airborne particles, available for wider dispersion, will be produced.
Other sources of infectious airborne particles
Sources of light particles wich may contain viable organisms
- Lyophilized cultures
- Dried bacterial colonies
- Dried materials on stoppers and caps of culture tubes and bottles
- Dried exudates Fungal and actinomycetes spores
- Dusts from animal cages
It must be remembered that even the larger particles and droplets, which do not evaporate rapidly, may be a source of infection by contaminating surfaces (direct or indirect contacts). By this way, non glove-protected fingers may be contaminated by genetically modified (or not) micro-organisms and then transfered to both mouth and eyes.
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