Monitoring stunning parameters

Once the ideal parameters are selected and programmed into a waterbath system, it is necessary to regularly and routinely check the equipment is consistently achieving these aims, using the control panel of the stunner and additional monitoring equipment. Operators must ensure that the minimum value of the range of current amplitudes estimated or measured, is at least the recommended or legally-required minimum current amplitude per bird.

EC Regulation 1099/2009* requires waterbaths to “be fitted with a device which displays and records the details of the electrical key parameters used. These records shall be kept for at least one year”.

*abattoirs with relevant equipment that was in use prior to 1 January 2013 have until 8 December 2019 to comply with Article 14(1) and Annex II of Regulation 1099/2009, including the requirement above. (Abattoirs, layouts or equipment constructed after 1 January 2013 must apply the requirements immediately.)

Stunner control panel

The frequency and the amplitudes of the total current and voltage passing through a waterbath must be clearly displayed by a large frequency meter, ammeter and voltmeter respectively. Meters must be positioned so they are visible to personnel, including the slaughterperson(s) responsible for checking effective stunning and for neck cutting, so they can clearly see whether sufficient current is passing through the waterbath, without leaving their post or having to turn around. For accuracy, meters should ideally be digital and display all parameters to two decimal places. The units should be clearly indicated, eg Hz or kHz, A or mA. Voltmeters and ammeters must also be capable of displaying correct voltages and currents in RMS, average and peak units, for all waveforms the system can supply; the control panel must automatically indicate which unit is in-use at any given time.

For each different bird type slaughtered, checks of the parameters should be performed at least once per batch, and certainly if the parameters are altered by the operator between batches. This is particularly critical for constant voltage, multi-bird waterbaths, which must be carefully adjusted to attempt to obtain the correct current amplitude per bird. For example, when operating a constant voltage stunner, the actual voltage required may in fact be greater than was estimated. Therefore, at the start of slaughtering each batch of birds, the ammeter must be consulted and the voltage adjusted, as necessary, until the ammeter meets the estimated target. Regular monitoring of the ammeter is key to determining the typical total resistance for each stunner and each type of bird processed; operators can consequently adjust their voltages, as appropriate.

It is important that operators are aware what an ammeter reading refers to. Most ammeters record the total current flowing through the entire waterbath system (not through each individual bird). An estimate of the current supplied to each bird can be manually calculated by dividing the total current by the number of birds within the water at any given time. However, this method will not provide an accurate estimate of the current per bird because a) the number of birds in the water at a given time varies with moving shackle lines and shackling practices, and b) there may be variation in the total resistance of each branch of the circuit (eg the waterbath equipment, each individual bird and the quality of the electrical contact).

In an open circuit (ie with no birds in the electrified water), the ammeter of the stunner control panel should read 0 A. If the ammeter reads a value greater than zero, either the ammeter needs recalibrating, or current is being lost somewhere within the circuit. In each case, birds are at risk of receiving a lower-amplitude current than intended. An electrician must, if necessary, adjust the control panel ammeter and/or identify if, and where, the loss of current occurs and prevent it (eg by replacing corroded electrodes or connections).

Please refer to the HSA Guidance Notes No.7 on ‘Electrical Waterbath Stunning of Poultry’ if additional detail is required.

Additional monitoring equipment

In-line, stand-alone meters, or remote stun monitors (Figure 13), calculate the estimated current per bird more objectively and can also confirm the stunner control panel meters are accurate. Remote stun monitors can record the waveform, frequency, peak and RMS voltage and current. The device is essentially a resistor that simulates the resistance of a bird. A stun monitor can be shackled in place of a bird and passed through a waterbath either on its own or with live birds in other shackles (the latter scenario will reflect normal processing). The stun monitor records and displays the current amplitude flowing through it and the duration of application.

Figure 13. A remote stun monitor. This equipment simulates the resistance of a live bird and provides an estimate of current amplitude received per bird. Image: AGL Consultancy Ltd.

When estimating the current amplitude per bird using either the stunner control panel display or a remote stun monitor, there is a degree of error involved because of the assumed value of resistance. Therefore operators are strongly encouraged to also use, at regular intervals, a device that can measure [during normal processing] the actual bird’s resistance and the actual current amplitude passing through that bird (Figure 14).

Figure 14. A stunner evaluation device. This equipment measures the actual parameters passing through a live bird. Images: Paul Berry Technical Ltd.

Please refer to the HSA Guidance Notes No.7 on ‘Electrical Waterbath Stunning of Poultry’ if additional detail is required.

Next: Indicators of the effectiveness of stunning