RH | Rotronic

Not clear on what water activity is? Check out our other posts on water activity here!

Water activity affects a wide range of products from pharmaceuticals to foods, here we take a brief look at five typical applications where water activity measurements are used.

Remember water activity affects biological, chemical and physical properties of products.

Application 1 – Food

Water activity is critical in food production, reducing water activity reduces the available moisture for spoilage organisms to utilise as such low Aw can limit or prevent growth and spoilage.

Aw is often used to screen raw ingredients or end products to confirm that they are within tolerance. Aw measurements only take a few minutes and can therefore provide immediate feedback. This can save time, money and prevent health risks or product spoilage.

Aw can be used as an excellent indicator of shelf life. Once a production process has been fine tuned to deliver products with suitable shelf-life, online aw measurements can confirm production consistency.

Classic methods to control Aw in food are listed below.

Application 2 – Paper

Water activity or %equilibrium relative humidity in paper may not be your first thought, but the impact of poor or changing ERH in paper can be very costly. Changes in ERH can cause paper to curl or lead to increased static both of which can cause paper jams. For an industrial printing company this can lead to costly downtime. ERH also affects the binding of inks, drying times and ultimately spoilage by moulds and fungi.

Application 3 – Pharmaceutical Products

Drug production and storage is one of the most highly regulated manufacturing sectors. All stages of drug production, storage and delivery rely on critical control of many factors including water activity. Most drugs must be stored in stable conditions hence the advanced moisture impermeable packaging used. Aw readings as well as humidity monitoring and control are utilised to ensure free water is maintained within tolerance.

Application 4 – Seed preservation and storage

Seeds present an interesting challenge, if Aw is too low the seeds quickly become non viable, where as too high and they may germinate or suffer spoilage through mould or fungal growth. One of the most critical seed preservation projects is the Millennium Seed Bank project. More details about how Rotronic AW meters were used is avaialble on the Kew Gardens website

Application 5 – Soaps and powders

Finally we come to good old washing powder, even with powders and liquids now packed into clever tablets and pods Aw remains critical. The materials must be stored in a way that ensures safe delivery to the customer but can be released once in contact with water in your washing machine. The science of behind the latest washing powders and liquids relies heavily on the measurement and conrtol of water activity and %ERH!

Hopefully this brief in site into how water activity affects so many day to day products has been useful. For more information visit our website or contact us to discuss!

Dr Jeremy Wingate
Rotronic UK

Control of Temperature and Humidity in Hospitals

Temperature and relative humidity affects the airborne survival of viruses, bacteria and fungi. Thus environmental control in hospitals is important because of infectious disease transmission from the aerosol or airborne infection.

Environmental exposure is a common hazard for all such organisms (whether viruses, bacteria or fungi) during this journey between hosts. Factors such as temperature, humidity (both relative and absolute), sunlight (ultraviolet light) exposure and even atmospheric pollutants can all act to inactivate free-floating, airborne infectious organisms.

Maintaining hospital premises at a certain temperature and a certain relative humidity (%rh), likely to reduce the airborne survival and therefore transmission of influenza virus. Temperature and RH settings in different parts of a hospital differ slightly between summer and winter. In summer, the recommended room temperatures range from 23°C-27°C in the ER (emergency room), including in-patient and out-patient areas, as well as X-ray and treatment rooms and offices. The corresponding recommended RH is fairly constant throughout the hospital, between 50- 60%rh. In winter, the recommended temperatures are generally slightly lower, ranging from 20°C in some in-patient and out-patient areas, as well as offices, up to 24°C -26°C in in-patient and out-patient areas.

The recommendations for the newborn baby and the hydrotherapy treatment rooms are higher at 27°C –28°C. Again, the corresponding recommended range of RH is fairly constant, but slightly lower than for summer, ranging from 40%rh -50%rh, but up to 55%rh–60%rh for more critical areas, such as operating theatres and recovery, the intensive care unit and childbirth/delivery suites.

Temperature is one of the most important factors affecting virus survival, as it can affect the state of viral proteins and the virus genome. Virus survival decreases progressively at 20.5°C –24°C then < 30°C temperatures. This relationship with temperature held throughout humidity range of 23%rh- 81%rh.

Facts & figures:

RH (expressed in percentage) describes the amount of water vapor held in the air at a specific temperature at any time, relative to the maximum amount of water vapor that air at that temperature could possibly hold.

At higher temperatures, air can hold more water vapor, and the relationship is roughly exponential—air at high temperatures can hold much more water vapor than air at lower temperatures.

Why do we need to measure relative humidity?

Virus: The survival of viruses and other infectious agents depends partially on levels of RH. At a temperature of 21°C, influenza survival is lowest at a mid-range 40%rh–60%rh. It is also important to note that temperature and RH will always interact to affect the survival of airborne viruses in aerosols.

At High temperatures < 30°C and at high RH < 50%rh may reduce the survival of airborne influenza virus.

Bacteria : For bacteria, the effect of carbon monoxide (CO), enhanced the death rate at less than 25%rh, but protects the bacteria at higher RH ~ 90%rh.

Temperatures above about 24°C appear to universally decrease airborne bacterial survival.

Fungi: Ventilation systems controlling Temperature and Humidity have a significant effect on indoor levels of airborne fungi, with air-handling units reducing, but natural ventilation and fan-coil units increasing the indoor concentrations of airborne fungi.

Dehumidification as well as HEPA filtration can be used to improve indoor air quality.

Different airborne infectious agents (i.e. viruses, bacteria and fungi) will have differing conditions under which they may be optimally suppressed; it will need to be decided which airborne pathogen poses the most risk to patients and staff alike in hospitals.

Thus, in reducing infectious disease transmission specific environmental control of temperature and humidity is vital for hospitals and healthcare premises.

Rotronic can offering a complete system for hospital measurement applications: a proven system that enables healthcare facilities to control and monitor their conditions and remain in conformance with internal or regulatory guidelines.

With the combination of both analogue outputs, controlling the air-conditioning, and digital outputs, linked up to the Rotronic HW4 monitoring software, end users have a clear overview of conditions.

Dr. Jeremy Wingate
Rotronic UK

Rotronic – BLOG

Tag Archives: RH

Five Applications where Water Activity is critical and why!