Its use banned in warfare by the 1933 Chemical Weapons Convention, tear gas attacks the pain sensing nerves in the cornea of the eye, the nasal passageways and throat leading initially to intense mucous secretion, blockage of the airways, chocking and confusion and subsequently to skin burns and vomiting and even death.

When properly deployed in a limited amount in open areas against healthy young people uneffected by asma or other ailments, there is yet no evidence of long term effects, however in Cairo police repeatedly fired large numbers of tear gas canisters directly at crowds in the narrow streets and alleyways.

In the photo you will notice that the goggles and medical masks the protesters were wearing appeared to have offered little or no protection. I saw numerous people chocking - and several protesters who appeared to be unconscious and others suffering from shaking and convulsions.

When protesters later collected the empty canisters they discovered that many of them carried dates that proved they were from outdated stocks making them far more toxic and lethal. Also, some activists claimed that the riot police were using either more toxic forms of tear gas or possibly CR gas or other poisonous nerve agents.

Three months earlier, In November 2011, during between security forces and protesters, the American Embassy had tweeted

“U.S. security assistance funds were not used for tear gas. That’s a genuine fact.”

However there was no hiding the fact that the U.S. government was granting a license to at least one American company to export tear gas to Egypt and a shipping manifest obtained by the Egypt Independent showed that Combined Systems Inc had indeed been granted a license to sell tear gas directly to Egypt's Ministry of Interior.