Quarantine reading inside, might prevent the test subjects to open the hatch, if they thought quarantine is being outside of the hatch.
Interesting to me - the Hatch door was highlighted twice in the season finale, once by Eko after climbing out of the Swan, and then as the only piece of debris that landed on the island after "the incident" ... 04:37, 26 May 2006 (PDT)
We have no way of determining when the Quarantine stenciling was done. Perhaps the Quarantine was established in reaction to the Purge, recognizing the hazard posed by the gas used by the Hostiles, coupled with uncertainty as to how long it would remain lethal. --ConspiracyofDetails 07:23, 14 May 2007 (PDT)