A hypothetical extraterrestrial sample (glowing core, centre) sheds
microorganisms that random-walk outward through a series of nested
containment barriers — the same "break-the-chain" logic proposed for
Mars Sample Return and used for the 1969 Apollo Lunar Receiving
Laboratory quarantine. Each barrier independently has a chance to
filter/block a particle that reaches it. A particle only escapes the
facility (turns red) if it slips past every layer.
P(escape) = (1 − e)^N
e = per-layer filtration efficiency (fraction)
N = number of barrier layers
- Barrier layers — how many independent containment shells
(airlocks, HEPA stages, biosafety cabinets) the sample must pass through.
- Filtration efficiency — chance each single layer blocks a
particle that reaches it; real BSL-4 airlocks and HEPA filtration
individually reach 95–99.97%.
- Sample emission rate — how fast the sample sheds
particles, i.e. how quickly the containment system is stress-tested.
- Breach button — knocks out one random barrier for a few
seconds, showing why redundancy (not a single "perfect" wall)
is what real planetary-protection protocols rely on.
This mirrors real biosafety and planetary-protection engineering:
no single barrier is ever assumed perfect, so facilities stack several
independently-failing layers until the compounded escape probability
drops below an acceptable threshold — the same principle behind
proposed Mars sample-return "receiving facilities" today.