Death caused by hyperthermia. This questionable method has been developed as a last resort option in case of a large-scale outbreak of High Pathogen Avian Influenza in the UK. Even in EU Regulation EU 1099/2009 there is room for countries to use this kind of methods, when compliance is likely to affect human health or significantly slow down the process of eradication of a disease. (EU 1099/2009; article 18, under 3). Hyperthermia means that the cause of death is overheating the shed of the birds. The normal core body (CB) temperature of a bird must remain within a narrow range around a mean value of 41.4°C if its welfare is to be safeguarded. If the core body temperature rises above 45°C most poultry will die quickly. To ensure VSD is effective the temperature in the house must rise to 40°C or greater and remain at that level. Maintaining a relative humidity of at least 75% will help speed the onset of death through hyperthermia. This DEFRA document provides procedures and instructions on using Ventilation Shutdown (VSD) as an emergency method of killing of poultry for disease control purposes.

1. www.defra.gov.uk
GUIDELINES FOR KILLING POULTRY
USING VENTILATION SHUTDOWN (VSD)
September 2009
Version 9

2. A.
Introduction
1.
This document provides instructions on using Ventilation Shutdown
(VSD) as an emergency method of killing of poultry for disease control
purposes as permitted under Schedule 9, paragraph 2 of the Welfare of
Animals (Slaughter or Killing) Regulations 1995 as amended.
2.
Authority to use Ventilation Shutdown (VSD) will not be given unless
Highly Pathogenic Avian Influenza (HPAI) infection has been confirmed. VSD
can only be used as a last resort. All other permitted killing methods must be
explored and discounted first.
3.
VSD must not be used unless written authority has been obtained from
the Secretary of State. VSD cannot be used in Scotland or Wales. The
National Disease Control Centre (NDCC) Joint Co-ordination Centre (JCC)
Field Operations Team will inform the Local Disease Control Centre (LDCC) in
writing when written authority has been given by the Secretary of State. It is
anticipated that it could take up to 24 hours (although every attempt will be
made to speed the approvals process up) to obtain written approval from the
time the Field Report (see VO/ROD Instructions on the Preparations of a Field
Report on the Suitability of Buildings for Whole House Gassing (WHG) or
Ventilation Shutdown (VSD) to Kill Poultry During an Outbreak of Highly
Pathogenic Avian Influenza)) is submitted to the NDCC. Where VSD is used it
can only be undertaken under the “direct supervision of an official of the
Secretary of State”.
4.
The aim is to quickly raise the temperature inside the house to 40°C or
more within 30 minutes of the commencement of VSD operations by sealing
the house, shutting down the ventilation and introducing heat (using
supplementary heaters if required to achieve a rapid increase in temperature)
and then maintaining that temperature for a minimum of three hours.
5.
Death is caused by hyperthermia. The normal core body (CB)
temperature of a bird must remain within a narrow range around a mean value
of 41.4°C if its welfare is to be safeguarded. If the core body temperature rises
above 45°C most poultry will die quickly. To ensure VSD is effective the
temperature in the house must rise to 40°C or greater and remain at that
level. Maintaining a relative humidity of at least 75% will help speed the onset
of death through hyperthermia.
6.
The results of modelling show that in optimum conditions for VSD, the
time taken for 2kg broiler chickens to reach a lethal CB temperature of 45°C
with supplementary heating supplied is 35 minutes. This assumes a leakage
rate from the building of no more than 2 air changes per hour, an ambient
temperature of 10°C and an ambient humidity of 70%. If day old chicks are
substituted for 2kg broilers, then the time to reach a CB temperature of 45°C
is 40 minutes with heaters operating.

3. B.
Pre killing planning
7.
VSD should only be supervised by staff who are fully briefed on the
VSD operating guidance and associated instructions. An Animal Health /
Defra official must be nominated by the LDCC to undertake direct supervision
of the VSD process.
8.
It is anticipated that a team of at least 6 people will be required to seal
a medium size poultry house and to install monitoring equipment and
supplementary heaters (if required). The number of people required will
depend on the type of ventilation system, the age and size of the building.
9.
Where supplementary heaters are required the heaters used must be
fan assisted, mobile, portable, have a self contained fuel supply and have a
fuel capacity of at least 3 continuous hours. The unit must be equipped with
the facility to allow remote thermostatic control (see more detailed
specification at Annex A).
10.
The coldest and draughtiest areas of the house are usually the end
walls due to catching doors and the recent preference for tunnel ventilation
where large fans are located. Heat will first migrate towards the roof space
and then along the length of the house, heating from the ceiling downwards.
Fan assistance from the heater is important for heat distribution. One heater
must be located near each end wall, regardless of the further numbers that
may be needed. To ensure good heat distribution there must not be
excessive distance between the remaining heaters. This may require the use
of several smaller heaters rather than a more limited number of higher
capacity heaters. Further guidance on the location of heaters inside the house
is given at Annex B.
11.
Heaters will require a power supply. Where the site supply is not
suitable backup generators will need to be provided (See Annex C). In
addition temperature control and monitoring equipment will be required (See
Annex D).
C.
Sealing the house
12.
The building must be sealed sufficiently to ensure it is reasonably air
tight. This will help ensure the quick build up of heat inside the building
following VSD. Poultry houses are designed with ventilation systems to
provide for the welfare of the stock and these systems have large numbers of
fans and ventilation inlets. They are not air tight and frequently there are gaps
around door frames, in the structure of the dwarf walls and often between roof
and wall panels. Newer buildings tend to seal better than older ones. There
are two components to be considered when sealing the building:
sealing the ventilation inlets/outlets and
sealing significant gaps in the structure of the building (e.g. gaps
between doors and walls, holes in walls).

4. Wherever possible the house must be sealed from outside to minimise
exposure of personnel to infected birds and contaminated material.
13.
Materials that can be used for sealing include:
Heavy gauge plastic sheet (e.g. as used in the construction industry
to form a water impermeable membrane in floors)
Wooden battens (approximately 20mm x 5mm is adequate) to secure
the plastic sheet,
Nail guns and nails to secure battens (including spares to replace
those that will jam/malfunction),
Expanding foam (e.g. as used in the construction industry to fill gaps
in walls between pipes and brick work etc)
Duct tape
14.
Poultry buildings are normally force-ventilated. Air may be drawn in
through the walls or less commonly the roof and extracted, by fans through
the walls or roof. The inlets and outlets normally have housings (e.g. ducts or
so-called ‘boxes’) associated with them that are external to the building. More
modern ventilation inlets (e.g. Skov-type) may have dampers/deflectors that
adequately seal the inlets. Older systems or systems that have inlets that
cannot be sealed using the equipment fitted will need to be sealed by
alternative means.
15.
Sealing fan boxes using plastic sheet and battens is done most
efficiently if teams work in pairs (assume approximately 3 - 4 minutes per box
if all materials are to hand). Buildings can be prepared in advance as long as
adequate ventilation is maintained until VSD commences.
16.
All significant holes (e.g. larger than 25 cm2) in the walls/doors or
exposed drains should be sealed. Plastic sheet should be used, if required to
seal any significant gaps between doors and the walls etc. Ensure that all
doors are securely closed.
17.
A control point should be established. This should provide shelter from
the elements, light, power and space to conduct briefings. It should also allow
easy access to monitoring equipment.
D.
Sealing the ventilation system
18.
Wind blowing across fan ducts on the roof of the building (or other
similar apertures) will tend to draw air through the building reducing the
temperature inside the house. Inlets set in the side walls may have flaps or
dampers that can be positioned to seal the aperture. Inlets that do not have
this arrangement and side (wall) outlets (which are unlikely to have this
arrangement) will need to be sealed using plastic sheet and battens.
19.
Most ducts set in the roof will have dampers, boxes or similar that can
be winched into place. It is unlikely to be feasible to seal ventilation ducts set
in the roof beyond using the dampers, boxes etc that are already available.

5. 20.
The ventilation system should not be sealed until immediately prior to
full VSD however fan boxes can be sealed on three sides well in advance with
the final side, that closes the gap over the duct, being secured when required.
21.
The drinking system for the birds must not be shut off during VSD.
E.
Supplementary heating
22.
House heaters should be switched on and set to operate at their
maximum capacity during VSD. It might be necessary to override thermostat
settings where these are set to turn the heaters off at a temperature below
40°C. The aim is to quickly raise the temperature inside the house to 40°C or
more by sealing the house, shutting down the ventilation and introducing heat,
using supplementary heaters if required and then maintaining that
temperature for a minimum of three hours. Supplementary heaters will switch
off when the house has reached 40°C. The results of modelling show that in
optimum conditions for VSD, the time taken for 2kg broiler chickens to reach a
lethal CB temperature of 45°C with supplementary heating is 35 minutes. If
day old chicks are substituted for the broilers then the time taken to reach a
CB temperature of 45°C is 40 minutes.
23.
The NDCC JCC Field Operations will inform you of the supplementary
heating capacity and number of heaters required. This assessment will have
been made by the NDCC JCC Field Operations Veterinary Adviser in
collaboration with the Defra Animal Welfare Team VA. The assessment will be
based on the information provided in the field report, typical heat loss figures
for poultry units and modelling data. Additional preparation time should be
allowed where a large number of supplementary heaters have to be installed.
24.
Calibrated temperature sensors should be installed at bird height in
open floor based systems. For caged birds sensors should be placed in
bottom / middle and top row cage positions. Ideally in medium to large houses
there should be four sensors, one for approximately every 20m of house
length.
F.
Other preparations
25.
Ensure that there is enough suitable leak proof transport available on
site (or big bags) to take all the carcases. This is dependent on numbers and
the disposal method.
26.
Ensure there are sufficient trained staff available to kill any birds
remaining alive at the end of the VSD period and that there is sufficient
equipment available to complete this task as quickly as possible.
27.
Ensure personnel are available to disinfect the carcases and to load
them into bags or a leak proof transport container. It will be particularly
important to remove carcases as soon as possible after VSD has been
completed as the elevated temperature involved will result in very rapid onset
of decomposition.

6. G.
VSD process
28.
At the commencement of VSD all remaining gaps should be sealed and
all fans turned off. It may also be necessary to disable failsafe systems and
alarms etc. designed to prevent accidental ventilation shutdown. When
sealing the house, the system fan outlets at opposite ends of the building
should be switched off last to maximise airflow across the birds immediately
prior to the commencement of full VSD. Supplementary heaters / in situ
heating systems should be turned on at their highest setting. The house
should remain sealed for 3 hours and no one should enter the house during
this period.
29.
Monitor the temperature reached inside the house continuously.
Record the temperature at the start of VSD and record the temperature at half
hourly intervals whilst VSD is in progress.
30.
Maintain VSD for 3 hours. At the end of this period the heaters should
be turned off, vents should be uncovered and the ventilation system restarted
to cool the house and vent any build up of ammonia.
31.
Once the temperature inside the house has dropped below 30°C staff
can enter the house. Birds should be inspected for signs of life and any
surviving birds killed. Killing should be undertaken humanely using neck
dislocation or other permitted method.
32.
Once all the birds are dead enter the house and spray carcases with
disinfectant.
33.
Load carcases into bags / leak proof container for disposal.
H.
Post VSD report
34.
A post VSD report using an EXD 64 form should be sent by the LDCC
to NDCC and Defra AW Core Team within 24 hours of completion of VSD. In
addition to the normal comments and observations the following data should
be included:
heaters used
the capacity of the in situ / supplementary heaters used
the measures taken to ensure the effective application of VSD
duration of VSD
ambient temperature and internal house temperature immediately
before VSD commenced
the temperature reached inside the house taken at half hourly
intervals
the approximate number of birds found alive at the end of the 3 hour
VSD period
the condition of those birds remaining alive at the end of the VSD
period (conscious / unconscious etc.)
the method used to kill any birds remaining alive

7. recommendations to enhance the effectiveness of VSD
Checklist Of Equipment
Polythene sheeting or other material to seal the house
Wooden battens 20mm x 5mm
Nail guns, nails and spares
Expanding foam
Duct tape
Supplementary space heaters (where NDCC Animal Welfare Team
have advised the need for additional heaters)
LPG / Fuel for supplementary heaters
Generators to power heaters (if site supply not adequate)
Fuel for generators
Control equipment
Temperature sensors and monitors
Leak proof transport containers / big bags
Disinfectant / knapsack sprayers
Percussion or other permitted humane killer
For each operator
Respirator (typically FFP3 standard)
Safety goggles
Rubber boots
Other PPE – based on site and disease specific risk assessment
Key Reminders
Always wear Safety glasses and appropriate PPE
Always work with someone else and never on your own
Visual checks by trained staff must be undertaken immediately
after VSD is terminated to ensure that all birds are dead
Remove carcases as soon as possible
If something goes wrong notify the NDCC JCC Field Operations
immediately

8. Annex A
SUPPLEMENTARY HEATER SPECIFICATION
The basic specification for a suitable supplementary heater is as follows:
o Mobile – they must have wheels, however, the wheel should not be so
narrow as to sink into damp litter
o Portable – 2 adults must be able to lift the unit, despite the wheels, as
farms always offer obstacles. This limits the weight to about 70kg
o Self contained fuel supply – as it is not feasible to use on-farm LPG
supplies, supplementary LPG bottles should be provided or the heater
must carry its own fuel
o Fuel capacity - the fuel capacity must provide at least 3 hours
continuous running
o Type of fuel – The fuel required will be dependent on the heater type
selected. Gas fired heaters require bottled of LPG. Oil-based heaters
will use heating oil.
o Control – the unit must be equipped with the facility to allow remote
thermostatic control
o Fan assistance – the size of the houses and heat capacity demand
will require fan assisted heaters
o Capacity – the higher the capacity, the larger the unit, but the fewer
required. There will be a practical limit to capacity governed by the
portability of the heater and the need to ensure an even spread of heat
throughout the house
A call off contract is in place for the supply of direct fired gas heaters. The
operating characteristics are shown in the table below:
Wt
(kg)
28
G100TA
29
G260TA
Output
kW
102
77
Fuel
Kg/hr
7.3
5.5
Cyls
Kg
3x47
3x47
Duration Power
(hours)
(amps)
19
0.5
25
0.8
Thermostat
An example of a suitable oil fired heater is made by Thermobile. The
operating characteristics are shown in the Table below.
Wt
(kg)
48
TA 40
69
TA 80
Output
kW
46
93
Fuel
L/hr
4
8
Tank
L
80
160
Duration Power
(hours)
(kW)
20
0.43
20
0.83
Thermostat

9. To provide effective heat distribution, it is better to have more small units than
a few large ones to meet the heat requirements.
However, the setting up
time will be longer.

10. Annex B
GUIDANCE ON LOCATION OF SUPPLEMENTARY HEATERS
The coldest and draughtiest areas of the house are usually the end-walls, due
to catching doors and the recent preference for tunnel ventilation where large
fans are located. Heat will first migrate towards the roof space and then along
the length of the house, heating from the ceiling downwards. Fan assistance
from the heater is important for heat distribution.
One heater must be located near each end-wall, regardless of the further
numbers theoretically required. Also, if heat requirement only demands
3 heaters, but there is an excessive distance between the remaining heaters,
an extra heater should be used to ensure good heat distribution.
The basic specification for locating supplementary heaters is shown in Figure
1 (below):o One heater within 5m of each end-wall
o Minimum: 1 x heater per 20m house length, between end-wall
heaters
o Heater positioned approximately 3m from alternate side-walls
o Heat is directed across the house
Figure 1 – Location of heaters and temperature probes
< 20m
5m
5m
< 20m
3m
= heaters
= temperature probe
3m
=
Heat direction

11. Examples of heater distribution and layout
Example 1 - location and distribution for 5 heaters
Control
2 x HP15 Dual Zone controller
4 x probes
4 x heating zones
= heater
= temperature probe
40°C
40°C
= HP 15 Controller
= direction of heat
= heater separation
= <20m along house length
= <5 m from end walls
40°C

12. Example 2 - location and distribution
for 14 heaters
e.g. ‘Very large’ house (90′ x 360′)
3 ACH, poor insulation = 1250 W
14 x 93kW = 1300kW
Approximate centres: 9m
Extra heater at ends of the house where heat
loss can be greatest.
40°C
Control
2 x HP15 Dual Zone Thermostat
4 x probes
4 x heating zones
= heater
= temperature probe
40°C
= HP 15 Controller
= direction of heat
= heater separation
= <20m along house length
= <5m from end walls
40°C

13. Annex C
SPECIFICATION FOR BACK UP GENERATORS
Whilst poultry farms have ample power capacity to run fans and equipment,
with large back-up generators, they are notoriously badly supplied with power
supply points to run accessories. Most equipment is hard-wired and protected
from water ingress. What power points exist will be located in the control
room and in discrete parts of the house and have limited current capacity.
The requirement for multiple heater units that each demand a reliable power
supply, at short notice, will mean that is impractical in nearly all cases to
locate sufficient power supply points in the right location within the farm
To maintain an independent approach to the procedure, it is necessary to
provide portable generators. The basic specification for a suitable generator
is as follows:
o Portable – 2 adults must be able to lift the unit. This limits the
weight to about 40kg
o Self contained fuel supply – the generator must carry hold its own
fuel
o Fuel capacity - the fuel capacity must have at least 3 hours
continuous running at maximum capacity, assuming that the
generators are located in the houses. To ensure the generators are
functioning, can be replaced and have fuel, they should be located
outside the houses, with power supply leads running into the house
via sidewall inlets or fan shafts
o Power output - generators that are portable enough to use on a
farm are limited in power output. For any given KVA rating (volts x
amps), it must be assumed that only 70% is available to operate
equipment, due to power-factor corrections. A 3KVA unit will
provide:
3000 VA/240v
12.5 Amp x 0.7
=
=
12.5 amps
8.75 amps
o 1 x 3KVA generator could run 16 x G100TA heaters requiring 0.5
amps
o 1 x 3KVA generator could run 2 x TA80 heaters requiring 3.5 amps
(Note: it is always advisable to have at least two generators on site to
guard against possible equipment failure.
A suitable example is made by SIP, model Medusa 3KVA as described
below:-

14. Specification of a Medusa 3KVA generator
Wt (kg)
3KVA
37
Output
cont
3kVa
Fuel
Petrol
Tank
L
3.6
Duration
(hours)
2.6
Other generators of a similar specification would be suitable.
Power
(kW)
0.43

15. Annex D
TEMPERATURE CONTROL AND MONITORING EQUIPMENT
It is essential to have remote control of the heaters and remote monitoring of
the environment. Simple digital controllers are available. The basic
specification is as follows:
o Temperature registration – the unit must be able to monitor
temperature with a resolution to 0.1°C, with an easy-to-read display
o Temperature sensor - monitors via a remote digital probe
o Heater control – the unit must control the heaters in relation to a
set temperature. It must be able to adjust the heating bandwidth.
The heater and controller must be compatible and there must be
sufficient cable to link to the control unit along very large houses
o Zone control – Due to the size of poultry houses, more than one
sensor should be used. The control unit should be able to
accommodate more than one sensor. Ideally, in medium to large
houses, there should be 4 sensors, i.e. one zone for approximately
30m of house length
o Portable - to be portable, units will need a power lead and mounted
in a suitable panel or box
An example of a suitable control unit is an HP 15 – Dual zone thermostat
supplied by Climatec. This controller can monitor and control 2 heating zones
via two remote sensors. It can activate each group of heaters independently.
In large and very large houses, 2 units should be used, providing a total of
4 zones with its own temperature registration and control, and 4 outputs to
safely activate multiple heaters.
The temperature probes should be in the centre line of the house but between
the heaters, i.e. not in a direct line with the heater nozzles (see figure 1 at
Annex B above).