Latest report from M. Drahus, University of California at Los Angeles; Bin Yang, University of Hawaii; and J. Hoge, Joint Astronomy Centre, detect HCN (Hydrogen cyanide) in comet C/2010 X1 on July 30. Observations between July 30.153 and 30.249 UT at the James Clerk Maxwell Telescope show the J = 4-3 line with area about 0.1 K km/s in antenna temperature scale. Assuming an isotropic production of gas at velocity 0.5 km/s and a Boltzmann distribution of energy levels at 50 K, the derived HCN production rate is 1.5 x 1025 molecules/s, comparable to the mean level measured in comet 103P/Hartley at the same heliocentric distance in late 2010 (Drahus et al. 2011, Ap.J. 734, L4).
A concentration of hydrogen cyanide of 300 mg/m3 in the air can kill a human within 10 minutes. It is estimated that hydrogen cyanide at a concentration of 3,500 ppm (approximately 3,200 mg/m3) will kill a human in about 1 minute. Toxicity is caused by the cyanide ion, which stops cellular respiration by inhibiting an enzyme in mitochondria called cytochrome c oxidase.
Hydrogen cyanide absorbed into a carrier for use as a pesticide (under the brand name IG Farben Cyclone B, or German Zyklon B, the position B to Blausäure) was used by Nazi Germany in the middle of 20th century in the death camps. The same product is made by the Czech Republic under the name “D2 Uragan.” Hydrogen cyanide is also used in gas chambers employed in judicial execution in some U.S. states, which occurs during the execution of the action of sulfuric acid in the size an egg mass of cyanide potassium.www.newscorners
I have been Looking at 2005 YU 55 asteroid and they are calling it a NEO and it sure does pose a Potential , see the graph on the comets and asteroids Elenin , Levy, and 2005 YU 55 in this link that shows them all moving together in their orbits , http://www.ufo-blogger.com/2011/04/nasa-elenin-2011-comet-planetary.html
This must have prompted these actions Out of the Whitehouse last October , Source: http://www.whitehouse.gov/sites/default/files/microsites/ostp/ostp-letter-neos-house.pdf