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News archive - January 2019

Conflicting risks drive design

Conflicting risks drive design

Whether in a care home or hospital, handwashing and bathing are key daily tasks that help to aid recovery, preserve dignity, and prevent the spread of infection.

But, at the same time, there are serious risks involved in these seemingly-simple actions.

For example, to control the risk of Legionella, HSE guidelines suggest that hot water should be stored at 60°C and distributed so that it reaches a temperature of 50°C - 55°C in healthcare premises - within one minute at the outlets.

However, at these temperatures the risk of scalding is considerable.

These conflicting demands means the specification of fixtures and fittings is key.

“Hospitals and care homes need to blend the hot water to a safe temperature either using a centralised thermostatic mixing valve (TMV), or at the point-of-use”, explains Carole Armstrong of water controls specialist, Delabie UK.

Various modern anti-scaling technologies are available and choice depends on the associated level of scalding risk.

Maximum temperature limiters

Where scalding risk is low, Legionella control regimes must still be maintained. In healthcare facilities this means that hot water at 55°C is delivered to the point of use. Maximum temperature limiters are ideal for these environments. “The principle is to limit the amount of hot water that can enter the mixing chamber so that the pre-set maximum temperature is not exceeded. The user is unable to access the limiter and so cannot override the control,” explains Armstrong.

Pressure-balancing technology

In public areas within healthcare facilities, pressure-balancing mixers can provide an intermediate anti-scalding solution. The ceramic cartridge has an internal shuttle that continually adjusts to the incoming hot and cold water supply pressures to ensure a constant temperature at the outlet.

Thermostatic technology for high-level scalding risks

HSG 274 part 2 states that: “Where a scalding risk is considered significant … then type 3 thermostatic mixing valves (TMVs) that are pre-set and failsafe should be provided.” “Thermostatic technology ensures that the water is delivered at a constant, safe temperature regardless of temperature or pressure variations in the system”, explains Armstrong. “To failsafe, the hot water must shut off if the cold water fails and vice versa. This is where pressure-balancing cartridges and thermostatic cells differ. The latter is able to provide a complete failsafe to TMV type 3 standards.”

Sequential temperature control

One further consideration is user comfort. Showers and mixers with thermostatic sequential cartridges provide the user with complete control at the point of use. The valve opens and closes with cold water and the user can progressively increase the water temperature as desired up to a maximum pre-set temperature with one control. The risk of scalding is reduced considerably with the added benefit of drawing cold, potable water from the system.

Cool-touch technology

Some mixers also feature cool-touch technology. Traditionally the body and mixing chamber of showers and mixers/taps have metallic surfaces which are effective heat conductors. However, positioning the mixing chamber close to the hot water inlet avoids hot water travelling the length of the mixer body. Covering the mechanism and hot water inlet with an insulating material also reduces heat transfer. Similarly, circulating the hot water through narrow pipes inside the mechanism, with an air gap between the pipes and the brass parts of the mixer, also prevents heat conduction. If the mixer body is cool to the touch, the risk of burning through touching or accidentally brushing against the mixer is removed.

According to Armstrong, in recent years hospitals trusts have moved away from centralised TMVs to point-of-use thermostatic mixers for two key reasons:

“Their complex mechanisms slow the water velocity, resulting in biofilm formation and an increased risk of bacterial contamination”, he said. 

“Pre-blending the water reduces the cold water draw-off at the point of use creating a deadleg with stagnant water where bacteria can proliferate.

“The higher the scalding risk, the more-complex the mechanism is to reduce that risk, which comes with an increased risk of bacterial development.”

In this case, he advises installing the TMV as close as possible to the point of use, thus minimising cold water deadlegs and improving access.

“TMV3 approved valves must also be regularly checked to ensure that the failsafe is operating effectively,” he warns.

Offering advice to estates and facilities professionals, she said: “In hospitals HSG 274 requires the Water Safety Plan to identify the necessary procedures for managing Legionella. In care homes, a similar exercise must also be undertaken by the duty holder to comply with HSE guidance.

“For each point-of-use, the level of risk associated with scalding and Legionella control will indicate what technology is appropriate to ensure user safety.”

There are also other considerations in addition to user comfort and safety.

“Products must be fit for purpose,” said Armstrong.

“Patterns of use in hospital washrooms are very different to domestic applications. And, since the user is not the bill payer, products that feature sustainable technology, for example regulated flow rates and/or self-closing mechanisms will avoid unnecessary waste.

“The product must also be able to withstand intensive use and sometimes heavy-handed use over prolonged periods, although if the product is easy to use it will be subject to less unintentional vandalism.

“And products that are easy to install will save time and money, especially when budgets are under increasing pressure.”

Another consideration is the replacement cost of worn-out equipment.

Intensive use will take its toll on even the most-durable of materials, creating a natural lifespan for the products.

Lifespans can be extended through regular maintenance and the initial specification choice can have a considerable impact on the service life of a product.

“Standardised replacement parts simplify servicing and integrated filters protect the mechanism from system debris,” advises Armstrong.

“A quick check to see if the water controls incorporate these elements will reduce maintenance costs and extend the lifespan of the project.”

Standardised parts also mean that re-purposing points of use can be easily undertaken.

“Through the application of a risk-based analysis, and installing mixers that are appropriate to use; estates and facilities professionals can meet legislation requirements, ensure user safety, simplify their maintenance routine and guarantee continuity of delivery, even when wash stations and toilet facilities are re-purposed,” said Armstrong.

“Installing mixers and taps that are fit for purpose will ensure that patient/user safety is paramount and the risk of infection is minimised.”

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