Effects of ambient temperature and water vapor on chamber pressure and oxygen level during low atmospheric pressure stunning of poultry

Abstract

The characteristics of the vacuum used in a low atmospheric pressure stunning system to stun (render unconscious) poultry prior to slaughter are described. A vacuum chamber is pumped by a wet screw compressor. The vacuum pressure is reduced from ambient atmospheric pressure to an absolute vacuum pressure of ∼250 Torr (∼33 kPa) in ∼67 sec with the vacuum gate valve fully open. At ∼250 Torr, the sliding gate valve is partially closed to reduce effective pumping speed, resulting in a slower rate of decreasing pressure. Ambient temperature affects air density and water vapor pressure and thereby oxygen levels and the time at the minimum total pressure of ∼160 Torr (∼21 kPa) is varied from ∼120 to ∼220 sec to ensure an effective stun within the 280 seconds of each cycle. The reduction in total pressure results in a gradual reduction of oxygen partial pressure that was measured by a solid-state electrochemical oxygen sensor. The reduced oxygen pressure leads to hypoxia, which is recognized as a humane method of stunning poultry. The system maintains an oxygen concentration of <5% for at least 2 minutes, which ensures that birds are irreversibly stunned. Calculated pump down (pressure versus time) data match experimental data very closely because the programmable logic controller and the human machine interface enable precise and accurate control. The vacuum system operates in the turbulent viscous flow regime, and is best characterized by absolute vacuum pressure rather than gauge pressure. Neither the presence of broiler chickens nor different fore-line pipe designs of four parallel commercial systems affected the pressure-time data. Water in wet air always reduces the oxygen concentrations to a value lower than in dry air. The partial pressure of water and oxygen were found to depend on the pump down parameters due to the formation of fog in the chamber and desorption of water from the birds and the walls of the vacuum chamber.

Determining Candidate Hypobaric Hypoxia Profiles for Humane Killing of Laboratory Mice

“…The chamber is connected to a vacuum pump (DVP lubricated rotary vane vacuum pump, LC25 2018) by hose and proportional control valve to enable fixed decompression rates, adjustable according to cycle time or pressure thresholds (outlined fully in Table 2 ). In line with previous work ( 34 , 35 ), decompression profiles consisted of two distinct phases. Phase 1 involved decompression to a target pressure of 200 mBar (~11,800 m equivalent altitude) followed by a subsequent minimum hold phase (phase 2) for 5 min, which was extended in additional 1-min increments until confirmation of death (i.e., >30 s of motionless) as necessary.…”

“…When describing decompression, equivalent altitude is often used, for example ambient barometric pressure at sea level (0 m) is 101.3 kPa (1,013 mBar). In commercial LAPS, an equivalent altitude of 8,459 m (33.3 kPa; 333 mBar) is reached at an average rate of 127 ms −1 during the first ascent phase ( 35 ). However, there are notable differences between mammalian and avian anatomy and physiology, which could affect responses to hypobaric hypoxia.…”

Benefit of a single simulated hypobaric hypoxia in healthy mice performance and analysis of mitochondria-related gene changes

“…Continuous gas flow and CO 2 absorption by Ca(OH) 2 within the hypoxic chamber maintained CO 2 levels below 0.4% with continuous monitoring. According to the method described by Paul H Holloway et al 40 , the cabin pressure was adjusted to drop within 20 min to a vacuum of minus 11.01 kPa in the SHH 5000 group, which was equivalent to an altitude of 5000 m atmosphere force; and the cabin pressure was adjusted to drop within 20 min to a vacuum of minus 7.51 kPa in the SHH 8000 group, which was equivalent to an altitude of 8000 m atmosphere force. A control ambient environment for breathing 21% O 2 was created with an identical chamber setup.…”

Killing for purposes other than slaughter: poultry

“…In this method, broilers are placed in containers into the decompression chamber and are exposed to gradual decompression with a reduction of available oxygen to less than 5% (Martin et al., ,b,c; Holloway and Pritchard, ). This method was found to be acceptable based on the published scientific evidence only for broiler chickens up to 4 kg live weight.…”