Hospitals and Operating Theatres

There is growing awareness of the relationship between relative humidity (RH) and pathogens such as bacteria and viruses. This has important implications for the role of RH management in infection control – especially in healthcare and pharmaceutical facilities.

Viruses such as influenza and norovirus (the ‘vomiting bug’) survive longer at an RH of 20-30%, whilst a mid-range RH between 40% and 70% will minimise their survival rate. Also, tests indicate the infectivity of the influenza virus is increased by both low and very high RH, with minimum infectivity at 50% RH.

RH has been shown to have a similar effect on airborne bacteria, with a high mortality rate of airborne pneumococci, streptococci & staphylococci at intermediate RH levels.

When RH is persistently below 40% it causes moist tissues in the nose, throat and lungs to dry out, leaving the body susceptible to infections. Therefore, maintaining mid-range RH not only reduces survival rates of viruses and bacteria, it also supports the body’s infection resistance.

In an operating theatre, dry air will increase the rate of evaporation from tissues, thereby exacerbating problems of dehydration.  Low humidity can also result in static and the risk of ignition of medical gases and reliability of electronic medical equipment.

An RH range of 40-70% is considered acceptable for most workplaces and will also be suitable for most healthcare facilities – though it’s important to check specific regulations relating to particular areas in hospitals and other facilities.


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