Understanding the Benzene ring
"The benzene ring is a basic component of many organic compounds, especially the aromatic hydrocarbons. In benzene itself, each carbon atom is also bonded to a hydrogen atom; in derivatives of benzene, one or more of the hydrogen atoms is replaced by other atoms or groups of atoms."
How to bump test and calibrate gas detection equipment
ATEX, IEC, British HSE, and US OSHA standards all call for the bump test and calibration of any portable instrument used for worker health and safety protection in a potentially hazardous environment. In order to ensure safety it is necessary not only for the gas meter to read accurately but also to have functional alarms that alert the worker to a hazardous condition. Initial calibration upon receiving the instrument is necessary and, because most sensors can suffer decreased response over time, recalibration will be required.