Break Glass call point

Manual Alarm Call Points (MACs) allow an operator to initiate the emergency response system, regardless of the response of the automatic instrumentation. They can be used for any type of emergency. The typical MAC is of the open contact Break Glass type, suitable for Division 1 locations. MACs should be covered with a guard to prevent inadvertent alarm activation. They should be clearly visible and labeled and easily operable by personnel wearing personal protective equipment (PPE) such as gloves. 

The flexibility of amorphous polymers is reduced drastically when they are cooled below a characteristic transition temperature called the glass transition temperature (Tg). At temperatures below Tg there is no ready segmental motion and any dimensional changes in the polymer chain are the result of temporary distortions of the primary covalent bonds. Amorphous plastics perform best below Tg but elastomers must be used above the brittle point, or they will act as a glass and be brittle and break when bent. 

Water adsorbs into the walls of a glass container, but that adsorption is the extent of its adhesion. Some adsorbed molecules react chemically with some types of containers in a process called chemical adsorption (chemisorption. For example, carbon monoxide chemisorbs with palladium, but not with gold). The bonds resulting from chemisorption can hold molecules to the surface with far greater force than would exist with only physical attraction. It is also possible for a molecule (that normally would not chemisorb with the container wall) to break up when hitting the wall s surface. At that point the molecule s constituent parts chemisorb with the container walls. When an adsorbed gas reacts with the materials of a container, it is called reconstruction (for example, the reconstruction of iron with oxygen is rust). 

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