The indoor air of animal confinement buildings is heavily contaminated with gases and particulates (80c). Barn workers are continuously exposed to toxic manure gases. Even when ventilation systems are operating to specifications, air quality in hog barns, for example, may still present a hazard to both workers and animals (80c). Chronic exposure to manure gases is associated with serious physiological and neurobehavioral effects (see above). Elevated ammonia and dust levels in hog barns may also affect health of animals by increasing the severity of respiratory infections in promoting colonization of the respiratory tract by bacteria which cause atrophic rhinitis (80c) and other inflammatory reactions (76a). These reactions stimulate the cough reflex in hogs, which then presents the potential for aerosols that may disperse various pathogens, such as viruses and bacteria (see above).

In cold weather, barn ventilation rates may be reduced to conserve heat and electricity. Under such conditions, levels of ammonia and other pollutants to which animals and workers are exposed increase (66a). If a ventilation system fails for a few hours, toxicity of manure gases within the building can rise rapidly to lethal levels (80a). On the night of 14-15 November 2000, approximately 3000 hogs died in less than two hours near Sperling, Manitoba, when power to the ventilation system and the backup was cut off.

Manure gases such as ammonia, hydrogen sulphide and phosphine are toxic (39a, 134b). Methane is explosive (137a). The atmosphere in manure storage structures and tanks, and in some instances immediately above outdoor manure pits (80a), is lethal, because of the combination of toxic fumes and lack of oxygen. At least four people have died in Manitoba while attempting to service such structures, and many more have died in the United States, prompting the Centers for Disease Control and Prevention to issue a series of documents on the issue (e.g. 137a). Such fatalities may involve several people in the same incident, as fellow workers or family members enter the structure successively in an attempt to rescue their fallen comrades.

Death in such structures may be due to asphyxiation, as methane and other heavy gases displace oxygen in the structure ; oxygen is also depleted in the course of microbial decomposition of the organic matter in the manure. Hydrogen sulphide may cause instantaneous loss of consciousness or "knockdown", where the worker has no time to attempt to save himself. Similarly ammonia exposure may impair the worker's ability to escape from further exposure (134b). If the unconscious worker falls into the liquid manure, he may drown in it, as happened in 1989 in Ohio in the case of a dairy farmer (80a).

Airborne pollutants in barns are a serious concern with respect to the health effects on workers (155). Respiratory diseases are the most common form of occupational disorder in producers (39b, 39c, 39d, 155). Workers in intensive livestock confinement buildings are exposed to dust and endotoxin, particularly in swine barns (207a, 223, 224). Major constituents of swine dust are bacteria, mites, fungal spores and animal dander (155). Gaseous respiratory irritants include volatilized ammonia, methane and hydrogen sulphide (155)(see above). These contribute to both nonobstructive and obstructive bronchitis in barn workers. Endotoxin impairs lung function (155).

Organic dust toxic syndrome (ODTS) has been shown to affect pig farmers significantly more than the general rural population (224). ODTS is characterized by inflammatory conditions of the respiratory system, and decline in lung function is related to the amount of exposure (223). A study in Quebec (27) found that so-called "modern barns" have no advantage over "older and dirtier facilities" in terms of respiratory illness among barn workers. This study (27) concluded that "modern farming has not succeeded in making swine confinement buildings inoffensive to exposed subjects".

Workers in intensive livestock confinement buildings and meat processing plants are subject to a variety of occupational health risks. Aside from extensive exposure to pathogens, a number of industry-related illnesses can affect producers and employees. Workers in meat-packing plants suffer enormously high turnover rates because of the stressful conditions created by production pace demands that are too high and which increase the risk of accident. The punishing production rates result in inhumane or brutal treatment of animals as workers cannot ensure every animal is properly stunned or subjected to minimal distress and pain. A program in 2000 by Winnipeg CBC 24Hours revealed that 25% of workers in a large Manitoba meat packing plant sustained work-related disabilities, a rate substantially higher than in other industries, including mining. Such rates place disproportionately large demands on the health care system, social safety net programs and other services such as counseling for domestic dysfunction. The stepped-up production rates also increase the risk of contamination of the food products, as well as risk of zoonotic infection of the workers.

Hearing loss is commonly encountered among swine building workers, as the noise of a screaming sow can exceed 100 decibels.

Recommendations

$ Slaughterhouse employees must be allowed to work at safe and comfortable speeds.

$ Procedures which cause occupational injuries in slaughterhouse production lines must be reviewed.

$ Working conditions of barn workers must be reviewed and monitored. Dust masks and hearing protection must be mandatory. In some jobs, respirators may be necessary, as small dust particles and fungal spores may penetrate dust masks.