Despite this, activists have reported grave injuries as a result of tear gas canisters fired at protesters from close range. Moreover, the non-lethality of the gas is also in doubt, as serious questions are being raised about the causes of recent deaths during this week's protests in Cairo's Tahrir square...Two US companies have been identified as major exporters of the devices: Combined Systems Inc and NonLethal Technologies Inc, both based in Pennsylvania. [we invited Combined Systems and NonLethal Technologies to respond: NonLethal Technologies declined to respond; Combined Systems has not responded]