Because a white paper mask will help.

[HP-ILnerd]

The spent first stage of a (successful) Chinese Long March rocket lands near a village. 

http://spaceflightnow.com/2015/01/04/photos-long-march-rocket-stage-falls-in-rural-china/

I would think the obvious scary orange cloud of residual nitrogen tetroxide would be enough to keep gawkers away and from handling debris, but not so much.
The soldiers sent to guard the place look all safe too in what appear to be ordinary dust masks.

[SeanB]

1 billion replacements for them available pretty much off the shelf, so a few missing from incapacity is no worry.

[free_electron]

Her eis how china solved the pollution during the olympics :send half their population into bejing. every body breathe in , hold your breath while walking home. totally clean air in bejing..