The planning application for the chicken sheds includes a ‘Study’ by a Computer Modelling company.
The aim of this study is to predict the intensity and spread of odour produced by the chicken sheds once they are up and running. Once the sheds are operational, it will be too late to complain about smells so we have to rely upon computerised predictions to enable us to make an informed decision.
The Study is quite complex and uses a lot of mathematics to explain its findings. I aim to explain its findings using everyday language. Let’s start by considering what happens in just one of the sheds.
Where does the odour come from?
The chickens and their poo. On day 1 of the 45 day cycle, baby chicks have clean bedding and the smell is a minimum.
During the next 38 days, the birds will grow and the amount of poo they deposit will increase. The amount of odour produced will increase, not just steadily, but at an increasingly greater rate. By day 38 it will be about 8 times greater than on day 1.
After 38 days all the birds are removed and during the next 7 days the shed is cleaned out: this is when the production of odour peaks to its highest level, particularly during a 2 hour period when the shed is cleared out and hosed down.
All poo and spent litter is transferred by trailer to the storage area beside the Anaerobic Digester and covered with sheets. During this period the odour emission will be several times higher than at any time during the previous 6 weeks.
It should be noted that whilst each shed is cleaned out only once every 45 days, because production in the 4 sheds is staggered, there will be a shed clean-out on site every 11 days.
Where does the odour go?
Out of the shed roof. Fresh air enters the sides of the sheds and high-speed fans blow the polluted air out through the roof. The rate at which the odour is extracted from the shed depends on how fast the fans are running (the ventilation rate).
Is the rate of emission of odour polluted air steady?
No. The rate at which the fans blow out polluted air will vary considerably. On warm days it may be several times higher than on cold days. However, the amount of odour (smell) coming out of the roof will depend on both the intensity of the odour and the volume of air. A small volume of very smelly air is just as polluting as a large volume of less smelly air
How are odours measured and compared?
If you have an average sense of smell and are sitting in a clean room, you will detect an odour once its concentration reaches a value of 1 (more correctly; “1 European Odour Unit per metre cubed of air”). Whether the smell is a pleasant scent or repulsive odour is irrelevant.
If you are able to detect an odour against background odours in the open air then its level is between 2 and 3.
If an odour is recognisable (if known) then its concentration is 5.
If an odour is strong, persistent and intrusive then its concentration is 10.
Are all smells the same?
To humans, no.
Coffee roasting odours are classed as “less offensive”.
Intensive livestock rearing odours “moderately offensive”.
Decaying animal odours “most offensive”.
So, you might be happy to sit in a coffee shop where the coffee odour (“less offensive”) is at a high concentration level of 10 (strong, persistent). But you would be repelled by the smell of rotting animals (“most offensive”) even if its concentration was only 2.
What level of odour pollution is acceptable (according to the Environment Agency)?
An odour does not have to be continuous to be unacceptable. If it exceeds a “benchmark exposure level” for longer than 2% of the time, then that will be deemed unacceptable. This is an average of 2% over a whole year so could be: 1 minute an hour, 28 mins a day or 14 hours a month.
The odour concentration level chosen as benchmarks are:
1.5 for most offensive odours (rotting animals)
3.0 for moderately offensive odours (intensive animal rearing)
6.0 for less offensive odours (coffee roasting)
So, if computer modelling predicts that the concentration of odour from a chicken shed is over 3 for 28 mins a day, then that is “unacceptable odour pollution”.
Is computer modelling accurate?
There are limits to computer modelling but in general it is getting better all the time - witness weather forecasting and exit poles at Elections. Modelling the odour produced by the Cropwell Bishop chicken sheds takes account of wind speeds and directions, ambient temperature and terrain.
What does the computer modelling show?
If you drive (or cycle) by the chicken sheds on the old A46 road leading to Cropwell Butler, you can expect a strong, persistent, most offensive odour 28 mins a day (on average) of level 10. NB: you will be passing the dead bird shed as well as the chicken shed. This is 3 times higher than the “unacceptable odour benchmark”.
If you are driving down the new A46 (in either direction), or coming to Cropwell Bishop down the slip road from the A46, you will recognise a moderately offensive odour 28 mins a day (on average) of level 5. This is almost double the “unacceptable odour benchmark”.
If you are travelling along Nottingham Road or visiting the nearby garage, you can expect a moderately offensive odour 28 mins a day (on average) of level 3. You can expect the same if you take a walk along the Grantham Canal.
The modelling study states that "the population may be exposed to short term concentrations which are higher than the hourly average" and that "fluctuating odour is often more noticeable than a steady background odour".
The map showing these odour levels is displayed below. To download a copy of the Odour Study, click:
If you wish to submit a comment to Rushcliffe Borough Council regarding this planning application, go to their website:
and enter 17/01327/FUL as the keyword. You have until Monday 10th July.
Last night, the Parish Council voted to reject the Planning Application but that is just the first step in the planning process.