Since the October discovery of explosives from Yemen hidden in ink cartridges on cargo planes, the $50 billion freight business has seen little escalating security. Even in the midst of one of the air cargo industryâ??s busiest periods of the year, governments and aviation experts continue to struggle to come up with ways to strengthen cargo security without paralyzing a business essential to global trade. Cargo safety has suddenly emerged as one of the biggest topics in aviation security. Governments around the world have pledged to tackle the problem, while in Congress, lawmakers are calling for much tougher inspections of cargo. The cargo industry has resisted one idea: screening all cargo. It argues that such a step is impractical since most airports do not have the space to screen all the packages shipped each day. And some goods, including perishable products and medical supplies, may not survive a long wait at the airport to be screened. Air cargo can come from countless sources and comprises countless kinds of goods, including fresh produce, medical supplies and electronic devices. The cargo industry itself is fragmented, too, with door-to-door shippers like DHL, United Parcel Service and FedEx; all-cargo airlines; and shipping companies that rent cargo space on passenger planes. Air cargo represents about 40 percent of the value of global trade.