BSEE MEDICAL & HEALTHCARE


Building services engineers need to be aware that relave humidity plays an important role in infecon control in healthcare applicaons. John Barker of Humidity Soluons explains.


he relationship between humidity control and creating a healthy indoor environment in any building is well understood, though it’s true to say that humidity control is sometimes ‘value-engineered’ out of a project post-specification. In healthcare buildings, however, humidity control plays an even more significant role than in a ‘normal’ workplace, in terms of health and wellbeing.


T


This is because of the relationship between relative humidity (RH) and pathogens such as bacteria and viruses – a relationship that has become much better understood in recent years. This has important implications for the role of RH management in infection control in both healthcare and pharmaceutical facilities. To understand this, it’s worth considering the interactions that can occur between RH and our bodies’ resistance to infection, as well as the pathogens that may be in the air or on surfaces.


Infecon resistance


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 resistance to infection. Low RH is often associated with high levels of staff absenteeism, which can have a very negative impact on the performance of a clinic or hospital ward. Also, in an operating theatre, dry air will increase the rate of evaporation from tissues, thereby exacerbating problems of dehydration.


Surfaceborne infecons


uIn recent years there has been a trend to move away from the electrode boiler to resisve steam humidiflers as they don’t require replaceable boiling cylinders and therefore have lower running costs.


RH has an impact on the survival rates of bacteria on surfaces and maintaining the optimum RH can also facilitate more effective cleaning. For example, it has been found that survival of MRSA (Methicillin Resistant Staphylococcus Aureus) was significantly reduced when contaminated surfaces were stored at 45-55% RH, compared to 16% RH. Also, when RH is very low, static electricity can be an issue and raising the RH above 35% allows surfaces to become covered in a thin film of moisture that dissipates the static charge. This thin film of moisture facilitates more effective surface cleaning. It is also well known that some bacteria will form protective spores at an RH of less than 40%, making them more resistant to the actions of surface disinfectant.


Airborne pathogens


Viral infections are often spread through inhalation of contaminated air, resulting from actions such as speaking, coughing or sneezing. All of these actions can expel large numbers of ‘aerosols’, which are suspensions of solid or liquid particles in air, potentially including viruses. The smaller the particles, the longer


they remain airborne and the further they travel.


When these aerosols are exposed to dry air in a low RH environment, much of the moisture in the aerosol evaporates almost instantly, so the suspended particles become smaller and lighter and remain in the air for longer. This means the viruses can travel further in dry air, increasing infection risk across a wider area.


In more humid air the hygroscopic nature of these particles causes them to group into larger particles that fall to a surface more quickly, making regular cleaning of surfaces more effective. 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 and staphylococci at intermediate RH levels.


Controlling RH


For all of the reasons given above, an RH range of 40-70% is considered acceptable for most healthcare facilities (as well as most workplaces) but it’s important to check specific regulations relating to particular areas in hospitals and other facilities. For example, the Health Technical Memoranda (HTM) Guidelines 7.48 and 7.50 define the acceptable range of humidity as between 35% and 60% saturation. The Scottish Health Facilities Note 30 – “Infection Control in The Built Environment” notes that control and physical monitoring of humidity can help ensure that environmental conditions do not contribute to the spread of infection.


Problems relating to RH in the UK tend


to be because of low humidity. During the winter months buildings are usually heated to around 20°C and as the temperature rises the RH falls dramatically. For example, outdoor air at -5°C and 100% RH has a moisture content of 0.0025kg moisture per kg of dry air. When raised to 21°C dry bulb, with no humidification control, the resultant RH is a mere 18%. It's also worth noting that hospital wards are often maintained at higher temperatures than would be found in a standard work environment, thereby reducing RH even further.


Where comfort air conditioning is used in the summer months to reduce the temperature, the cold surfaces within the air conditioning system also remove moisture from the air, again leading to low RH.


Thus, humidity control usually requires the introduction of moisture using a humidifier to raise the RH. To that end, HTM 03-01 Part A Guidelines 3.55, 3.56 3.59 and 3.60 prefer clean, dry (central plant) steam for humidification. However, if that is not available a steam generator should be provided locally. It also states (Guidelines 4.91 to 4.115 and, 4.91 to 4.114) that only steam injection systems are permissible for humidification, and that water curtain, spray or mist humidifiers should not be used.


Building services engineers involved with healthcare projects will already be familiar with the need to acquaint themselves with the specific regulations that relate to these buildings. Given the potential complexity of humidity control in these environments it also makes sense to engage with specialists in the field of humidity control.


Steam for humidification can be generated in a number of different ways, using either electricity or gas to provide heat. Experience, therefore, plays an important role in arriving at the best solution. With the right balance of performance and cost of ownership.


www.humiditysolutions.co.uk 8 BUILDING SERVICES & ENVIRONMENTAL ENGINEER NOVEMBER 2018 VISIT OUR WEBSITE: www.bsee.co.uk


uThe relaonship between relave humidity and pathogens such as bacteria and viruses has become much beer understood in recent years.


Adversing: 01622 699116 Editorial: 01622 687031


REDUCING THE INFECTION RISK The importance of humidity control


‘


Viruses such as


infiuenza and norovirus (the ‘voming 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 infecvity of the infiuenza virus is increased by both low and very high RH, with minimum infecvity at 50% RH.


’


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50