Called at one of my regular pubs this morning. Noticed they had a new Co2 safety alarm fitted. I thought great but there is something wrong here. The Co2 detector was mounted 4ft off the floor and to cap it all this was fitted by their bottle gas supplier.
Wherever compressed CO2 is stored, especially in confined spaces like pub cellars CO2 safety alarms should be mounted 18 inches (45cm) off the floor. Because carbon dioxide is heavier than air, it will fill the enclosed cellar space from the floor up. Depending how bad the leak is, but if say a safety valve on a primary regulator is blowing off intermittently in a small cellar or room, CO2 levels can become life-threatening very quickly.
As for the safety alarm that is fitted 4ft from the floor it would be too late by the time that went off. I can see how the mistake is made by doing a quick search all over the google you will see searches bring up carbon monoxide alarms and they do need to be installed 4ft off the floor. Breathing air with increased concentrations of carbon dioxide gas can lead to effects ranging from heavy breathing and a feeling of suffocation through loss of consciousness to asphyxiation.