While OSHA’s portable fire extinguisher regulation at 1910.157(e)(2) does not explain exactly what “visual inspection” should consist of, a June 27, 1997, Letter of Interpretation says that the intent of the monthly inspection is to provide assurance that the extinguisher will operate effectively and safely. In addition to being in its designated place (readily accessible and immediately available), and being pressurized, the extinguisher should be observed for other possible defects, such as corrosion, mechanical damage, the presence of welding, soldering, brazing, or possible tampering.