Before the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) was created and implemented, there were many different regulations on hazard classification in use in different countries, resulting in multiple standards, classifications and labels for the same hazard.
Pneumatics Vs Hydraulics. The pros and cons of each system. Pneumatics offer a very clean system, suitable for food manufacturing processes and other processes which require no risk of contamination. Hydraulics is generally not used in these environments due to the risk of hydraulic oil leaks from faulty valves, seals or burst hoses.
This is really a poor explanation of the difference between a heat pump and an air conditioner. The thermodynamics are identical, and the fundamental difference between the two is that a heat pump uses a reversing valve and some additional plumbing to move the refrigerant in the opposite way through the two heat exchangers.