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14646

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will be split in an early part correlating more or less to the theory and a late part with a longer RT (Nilsson
2004 Part I + II).
RT is defined in ISO 3382-1 as the time it takes for sound source to decrease in level by 60 dB after thesource emission has stopped. RT is more commonly measured over a 20 or 30 dB range (T20 and T30) starting
5 dB below the initial level and then extrapolated to the full 60 dB range.
In healthcare facilities in many countries in Europe T20 is the only acoustic descriptor that is evaluated –and sometimes only in the mid frequency range. In comparison to T20 and T30 the rate of the first 10 dB ofthe decay is more related to the perceived reverberance and this can be measured by the early decay time(EDT) (Johansson et al. 2016, Keller et al. 2017).
According to the standard the evaluation of a measurement of T20 and T30 starts 5 dB below the initiallevel which can be problematic since this part of the decay contains a lot of information – both direct soundand early reflections – important for the perception of sound and speech clarity. The human ear analyses somuch more than the defined RT but the simplicity of the Sabine formula and the fact that only one single
number is ‘enough’ to describe the acoustic quality of a room might be the reason why RT – calculated (and/or
measured) – has been preferred for many years (Lochner and Burger 1964).
All this considered it is interesting to investigate how hospital staff is affected if not only reverberation
time is changed in a field study – and to see if very little differences in RT together with differences in values
on other descriptors will affect how hospital staff perceive the operation room (OR). In regards to criticalareas, like an OR, we know that there will be a different cognitive workload for different type of staff during
the surgery and that sound therefore will affect staff differently during the different stages of the operation(Keller et al. 2017). Knowing that hygiene demands in hospitals go before acoustic demands it is also verymuch interesting to learn if we with today’s disinfectable and cleanable acoustic ceilings and walls can makecritical areas more sustainable for the people working in them.

2. Working environment in a hospital
Hospital staff goes to work every day – to the hospital, clinic or other healthcare facility. In comparison
to the patients they are not sick and you would suppose that they feel a bit better when they open the door (!)– that they have maybe the opportunity to secure or react towards a healthy sound environment. Even though
the working environment in a healthcare facility is highly affected by sound and acoustics, staff isunfortunately not often aware of it.
A recent study about theoretical knowledge about sound and noise amongst staff revealed that 1047 staff
members answered in average 4 correct answers out of 10 on questions related to the impact of noise (in thequestionnaire some of the themes were chronic physiological changes related to noise, maximum levels
according to WHO, aconsaecute physiological changes related to noise) (Johansson et al. 2016). This could
tell us that even though staff members are ‘just’ at work (and not sick) they are not consciously aware of the
impact of noise on patients and themselves. And why should they – their competences are about saving lives.
We know from performance studies with office workers that sound pressure levels and room acoustic
conditions affect efficiency and wellbeing in general. A field study with a cross-over design by The StressResearch Institute and The Department of Psychology, Stockholm University, recently revealed that
improved sound environments were beneficial for health and performance together with less cognitive stressand less disturbances. Another interesting insight was that objective acoustic descriptors corresponded wellwith self-rated measures (Seddigh et al. 2015).
In hospitals communication errors can lead to fatal mistakes and in a cross-sectional survey with 84 nurses
in four hospitals in the Pacific Northwest region of the United States it showed that several physicalenvironmental factors were potentially problematic in the nursing station area and could lead to medication,
documentation, and other types of nursing errors. The most problematic factor according to the survey washigh noise levels (Mahmood et al. 2011).
In an advisory report based on healthcare staff reporting to the PAPSRS, Pennsylvania Patient Safety
Reporting System (USA) the same trend was documented and several examples of real-life medical errors
due to mishearing were published. Example: “A physician called in an order for ‘15 mg’ of hydralazine to begiven IV every 2 hours. The nurse, thinking that he had said ‘50 mg’ administered an overdose to the patient
who developed tachycardia and had a significant drop in blood pressure.” (Pennsylvania patient safety
authority 2006).
There is no doubt that hospital staff – like everyone else, is affected by sound, noise and acoustics when
they try to do their tasks, and it is highly important that acoustic standards and guidelines for healthcare
facilities are prioritized.
The World Health Organization recommends that since patients have less ability to cope with stress, the4647

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4650

5. DISCUSSION
The aims of the study were to see what would happen to room acoustic values if acoustics were altered in
two ORs and compared to an OR without acoustic treatment. The second aim was to see if the measured
acoustic descriptors would correspond with staff self-rated measures in regards to well-being, communication,
mistakes and impact of sound environment in general in the three rooms.
5.1

Room acoustic values
It is clear that when acoustics are altered in the two ORs room acoustic values change to the better.
But how much actually? When looking at fig. 2 we see only small changes on the general average values inall evaluated acoustic descriptors. The reason why we did this ‘average’ table is that this is often what the
project group often sees in a building process. You could most likely find people that would argument thatthe step from OR4 to OR5 in regards to RT has no consequences and that in Denmark it isn’t worth the money
nor the time to go from OR5 to OR6 event though the just noticeable difference for RT is 5% (Seraphim
1958).
In general, the results for the measurements show that there is an expected correlation between especially
T20 and C50 – but we have to look into the details to see the whole picture. The unexpected hops and drops
on STI are hard to explain – but another round of measurements could maybe be relevant. Overall there is no
doubt that the acoustic treatment makes the room acoustic quality from room to room better and when we
discuss all the parameters together the trend is clear. If we only look isolated on one parameter, we could
conclude that the changes are not really important – but the picture changes when all values are considered
together.
5.2

Reverberation time
If we take a look into RT based on the octave bands (fig. 3) we see a more detailed picture. We seethat the curve changes from OR4 to OR5 especially on the low frequencies (and that OR5 actually has astrange ‘hop’ on 125 Hz). OR5 would, despite, the ‘hop’ live up to the new Danish hospital standard – where
OR4 doesn’t. It is interesting though to see that even when adding the frieze of wall panels, the curve gets
more uniform and RT drops a bit more. Often, long RT on 125 Hz and 250 Hz are known to affect speech
intelligibility negatively (Canning and James 2012) which could be a problem in OR 4 (maybe OR5) and away of solving this could generally be to work in more dimensions than just the ceiling (which is actually
making the room more diffuse).
OR6 must be considered a good room in regards to RT – just below 0.6 sec. on 125 Hz and decreasing
on the higher frequencies. If we compare this actual room to a similar room in schools I Denmark – a grouproom meant for peer-to-peer work, group work or similar activities, the standard has a mandatory demand toreach 0.4 sec. (Bygningsreglementet 2008), which is exactly what this room does. We could compare theoperation situation to a ‘group work situation’/project based situation so even though the activities are verymuch different from a school situation to an operation event, it would make sense to discuss whether the newstandard for hospitals is actually good enough or if the demands should follow the mandatory demands foreducation facilities.
5.3

C50 and STI
When we look at average values on C50 and STI we don’t see a ‘straight forward trend’. On STI theacoustician chose to not have exactly the same distances from room to room and it ‘blurs’ the picture a bit. If
we look at distance OR4 1.9 m., OR5 1.8 m. and OR6 1.8 m. we see an expected improvement from OR4 to
OR5 but then it drops from OR5 to OR6 – yet still we see an improvement from OR4 to OR6 on the numbers
but they all fit in the ‘good’ level. On the longer distances OR4 2.6 m., OR5 2.4 m. and OR6 2.2 m. we see anegative drop from OR4 to OR5 – but a positive change from both OR4 and OR5 to OR6. Again all values
are in the ‘good’ level and therefore wouldn’t be considered to be really important changes. In comparison
to STI C50 shows a clearer trend. In fig. 3 we see values for 1 m. distance and from OR4 to OR5 to OR6 we
see an improvement every time we alter the room. On the distance 2.4 m. (not in the figure) we see an evenbigger change since OR4 shows 2.4 dB, OR5 3.7 dB and OR6 5.7 dB. This does not follow the trend for STI(that had a negative drop from OR4 to OR5) but shows that we have – for C50 – an improvement on +3 dB
from OR4 to OR6 that is quite remarkable. There is one common trend between STI and C50 though – and4651

that is that there always is a positive change from OR4 to OR6.
5.4

Dl2
The values for Dl2 shows a step by step improvement in general from OR4 to OR5 to OR6. It can be
discussed whether it is relevant to include Dl2 in this study since the rooms are 38.6-40.2 m2 and that special
decay then is less interesting. What we could say about Dl2 in this study is that we do have hard surfaces in
the room (the walls near the sound sources) and it would be difficult (and maybe not for the better) to have ahigher value. You still need some feedback from the room to secure that communication is not ‘lost’ fromone staff member to another across the room.
5.5

Questionnaires
The three questions chosen for this discussion show that there is a correlation between room acoustic
results and staff self-rated measures in regards to well-being, communication, mistakes and impact of soundenvironment in general. The trend is clear in regards to OR4, that this room is considered to be less popular.
For all of the questions this room stands alone when negative evaluations are done (keep in mind that thisroom actually lived up to the old acoustic guideline). The trend for OR5 and OR6 is a bit more ‘blurred’. The
overall tendency is that OR6 is most popular if we collect the scores in total and regardless the question, butwhen we look at each column for each question sometimes the best score goes to OR5 (considering the bestscore is the column ‘totally agree/disagree’). This can be seen in fig. 6. On the other hand, if we look closer
at fig. 6 and focus on the more positive columns together we see that OR5 takes a drop from ‘neutral’ to‘somehow disagree’ whereas OR6 takes the ‘expected’ hops from ‘neutral’ to ‘somehow disagree’ to ‘totallydisagree’. We need to keep in mind that the answers are not statically significant and that the questions
could be leading so these result only shows a tendency. It would be really interesting in the future to integratequestionnaires in room acoustic studies to learn more about what improvements on numbers actually means
for the end-users.

6. CONCLUSION
The overall goal of the study was to explore whether altered acoustics in operation rooms would affectthe staff and if yes in what way. Also, it was important for the study to investigate if evaluating more acoustic
descriptors would give a better picture of the room acoustic qualities than if RT alone was evaluated. The
overall conclusion is that an acoustic ceiling alone will improve room acoustic results but if we want constantpositive staff feedback/satisfaction we need also to add wall panels in the OR. When we include more
descriptors than just RT we get a better picture of what the sound environment can ‘support’. The activities
in an OR are complex and besides keeping the sound pressure levels as low as possible, speech clarity need
to be considered together with RT – and both STI (the subjective consideration) and C50 (the objective
consideration) have to be part of the evaluation. Spatial decay might not be really important in smaller ORs– but should definitely be evaluated in e.g. bigger hybrid ORs. Finally, it can be concluded that staff selfrated measures in regards to well-being, communication, mistakes and impact of sound environment
correlates with room acoustic improvements.

ACKNOWLEDGEMENTS
Without the engagement of staff and management at Hvidovre hospital this project would never havebeen possible. Also a big thanks to COWI and Tonio Stounbjerg, Saint-Gobain Ecophon Denmark for theircontributions.

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