Federal Motor Carrier Safety Administration (FMCSA) is issuing this safety advisory to provide notice to owners and operators of certain cargo tanks that they have been improperly inspected and tested, and must be re-inspected and retested before being used in Hazardous Materials specification tank service. The tanks in question were tested by H&W Tank Testing, CT#8083, Ohatchee, Alabama, and Christopher Humphries, CT#13131, Jacksonville, Alabama. Cargo tanks that have been inspected and/or tested by either company from April 2011 through March 2016, must be re-inspected and/or retested in accordance with 49 CFR § 180.407 immediately by a cargo tank facility registered with FMCSA.