Nitrogen dioxide (silo gas) poisoning in dairy cattle.

Toxic silo gases are a potential danger to livestock housed in close proximity to roughage silos. These gases, such as nitrogen dioxide (NO2), may be produced during the early stages of (maize and grass) silage making. In humans, inhalation of these gases causes a condition known as 'Silo Filler's Disease' (SFD), which is a recognized occupational hazard for workers in upright forage silos in many countries. NO2 accumulates on top of silage, is inhaled by workers, and reacts with water on the airway surfaces to form nitrous acid, which damages the lung and causes pulmonary oedema, bronchiolitis, and death in severe cases. On a dairy farm, a cloud of reddish-brown NO2 gas (which is heavier than air) was noticed to escape from underneath the plastic sheet of a horizontal maize bunker and to enter a cubicle house for dairy cows 1 day after ensiling. Eleven cows became dyspnoeic, 3 of which subsequently died. A combination of weather conditions, an insufficient sand load on the maize bunker, the utilization of a lactobacillus starter culture, and the close proximity of the silo to the cubicle house may have caused the incident.

An assessment of gases in oxygen-deficient hay silos and the effects of forced ventilation.

Many modern tower silos used in the agricultural industry for hay and grain storage are oxygen-limiting by design. Forced-air ventilation using a forage blower is a method commonly used to decrease concentrations of toxic and asphyxiant gases and to increase the O2 content within a silo headspace prior to worker entry. This article describes the methods used to measure gas concentrations and the results obtained from a pilot study by the Washington Fatality Assessment and Control Evaluation (FACE) program of two oxygen-limiting forage tower silos in eastern Washington State. The silos were monitored for oxygen (O2), nitrogen dioxide (NO2), and carbon dioxide (CO2). Measured O2 concentrations were low in all areas of the headspaces monitored for both silos. After beginning forced-air ventilation, O2 concentrations within the silo headspace returned to ambient levels within 8 to 20 min. Nitrogen dioxide levels exceeded the Washington Industrial Safety and Health Act (WISHA) short-term exposure limit (STEL) in the silo that was filled six days earlier (silo 2), but not in the silo that was filled four days earlier (silo 1). The NO2 concentration in silo 2 decreased to below the WISHA STEL within 15 min of starting ventilation but began to rise shortly after ventilation was stopped. Carbon dioxide, which was only measured in silo 1, was detected at 2% within the headspace of this silo. The carbon dioxide concentration decreased to <1% within 3 min of starting ventilation.

[Silo filler's syndrome]. / Siloentladersyndrom.

In 1975 an acute febrile bronchopulmonary illness after massive inhalation of fungal spores in silos was described as "pulmonary mycotoxicosis". Subsequently the disorder was referred to as "silo unloader's syndrome" or as a special form of "organic dust toxic syndrome" (ODTS). In this article the three cases of silo unloader's syndrome recognized by the Swiss National Accident Insurance Company (SUVA) between 1978 and 1989 as being an occupational disease are described. Two of the three patients with ODTS were wrongly diagnosed as suffering from allergic alveolitis and a change of occupation was proposed. Therefore, it is important to recognize ODTS in order to avoid unnecessary treatment and a change of occupation. ODTS can be prevented by technical measures such as prevention of mould formation and, in the case of exposure to fungal spores, use of an adequate breathing mask or a powered dust respirator helmet.

Gases in forage tower silos.

Measurements of hazardous gas concentrations in forage tower silos are described. The problems associated with sampling in silos, the identity and distribution of gases and their rate of evolution, and the effects of forced and natural ventilation are considered. Particular attention is given to conditions at times when entry to the silo by farm personnel is likely and the possibility of farmers carrying out gas measurements is discussed.