Hazardous materials inspectors have been inadequately trained and underfunded. Of the nine fires or explosions in passenger plane cargo holds that safety officials investigated from 1980 to 1988, for example, eight were caused by undeclared or improperly marked hazardous materials. While none of those accidents involved sabotage, the security issues they raise highlight how easily someone could put something dangerous into the cargo hold of an airliner. Every time you have an opening for a terrorist or someone who intends harm, if it's there, it will be exploited. General cargo, hazardous materials and mail each has its own security and safety systems.
None routinely involves physical inspection of shipments.
If we're serious about security, we have to screen everything and everybody. The shippers have to attest in writing that the shipments are safe, the logic being that if they know they will be held accountable if something goes wrong, they'll be more cautious about what they send. The small percentage of shippers who are unknown to freight forwarders is subject to a more stringent set of rules, including inspection of freight. The hazardous materials system also is based on document checks. Unless something spills during shipment, Federal Aviation Administration inspectors do not routinely inspect shipments.