Releases of ammonia (NH
), hydrogen sulphide (H S) and carbon dioxide (CO ) from deep manure pits were investigated in two overnight tests to minimize the in#uence of solar radiation and sudden outdoor temperature changes using two pig fattening buildings. The rooms of the buildings had been emptied and cleaned between groups of pigs. The identical buildings had tunnel and pit ventilation fans and 2)4 m deep under-#oor pits with a surface area of 800 m each. The "rst test was conducted in Building 3A. A new manure additive was applied in the pit to reduce gas and odour emission. The pit ventilation mode was used and the building was heated for about 1 h with one direct-"red propane space heater. The second test was conducted in Building 3B, in which the pit did not receive the additive application. The tunnel ventilation mode was used and the building was heated for about 2 h with two space heaters. Gas concentrations, ventilation, temperatures and di!erential pressure were continuously measured overnight. Gas release rates in the tests were compared with the gas release rates in the same buildings when they were fully occupied.
Ammonia release rates during heating were 167$11 g/h (mean$95% con"dence interval) in the "rst test and 46$2 g/h in the second test, equivalent to 65)5 and 24)9% of the rates from fully occupied buildings, respectively. The maximum H S release rates measured after 1 h of heating were 9)6 g/h in the "rst test and 3)1 g/h in the second test, equivalent to 80 and 41% of the full buildings, respectively. The maximum CO release rates after heating were 3)4 kg/h in the "rst test and 7)0 kg/h in the second test. Heating immediately increased NH , H S and CO concentrations and release rates in the under-#oor pits in both tests. Ventilation modes and rates a!ected the indoor gas concentrations at di!erent locations. Higher ventilation rate was related to higher gas release rate in the "rst test. A peculiar behaviour of H S characterized by burst releases was found in the two tests. It was a new phenomenon not yet reported in the literature and might be related to some unexpected incidents involving acute H S concentrations in animal facilities.