A myriad of factors are implicated in causing asthma in the workplace: the nature of the job being done, the location of the work site, the degree of exposure to irritants, and what kind of materials — vapours, fumes, as well as dusts — are being inhaled, among others. Various ways of defining asthma caused by work site conditions have been proposed but a newer classification system suggests two primary types of occupational asthma, asthma with latency and asthma without latency. Asthma with latency is precipitated by prolonged exposure (the latency period) to a substance present on the work site, which eventually causes allergic sensitization. This sensitization process eventually changes the way the respiratory and immune systems react, causing asthma symptoms. Asthma without latency occurs after only a single contact with an irritant substance that produces a sudden reaction that affects the airways without an allergic component necessarily being present. This leads to a condition called reactive airways dysfunction syndrome (RADS), which keeps the airways hyperresponsive.
To date, over 200 substances have been linked to occupational asthma with a latency period. Depending on the level of exposure, these triggers lead to asthma by precipitating immune responses characterized by IgE antibodies — the same function that sets off an allergic reaction to ragweed in many people.
Sudden onset of asthma (no latency period) can take place within minutes or hours of exposure, precipitate RADS, and can continue to cause asthma symptoms for years. In most cases, this kind of onset is due to an industrial accident, or ventilation of the workplace being compromised. Documented cases of such asthma attacks were triggered by uranium hexafluoride gas, spray paint with ammonia, fumigants, metal coating remover and smoke inhalation.
By-products of industrial manufacturing are heavily implicated in causing asthma symptoms. Allergic sensitization (associated with a latency period) is commonly caused by such materials as baking products and cotton dust. How much exposure is involved plays a large role in inducing symptoms of asthma, particularly in very dusty types of work. Polyurethane processing and foundry work are notable causes of asthma; millers and bakers exposed to grain dust have an asthma prevalence of up to 40%. If more hazardous activities are added to the list — pouring chemicals, blasting, sawing — the rate goes up even more.
Where the job site is located will affect asthma rates. For instance, western red cedar causes asthma in the western U.S., where it is native, and in Japan, where dock workers are exposed to it while unloading the ships that import the wood. An epidemic of asthma was caused in Barcelona, Spain, when a shipment of soybeans was unloaded in weather conditions that allowed dust from the beans to spread, demonstrating how climate conditions also affect the rate of asthma.
What can be done to reduce the risk factors for asthma in the workplace? Obviously, the ideal solution is to stay away from the kinds of employment that trigger asthma. As this is not always possible, employers should consider adopting strategies such as ensuring proper ventilation, providing personal protective devices (masks), rotating jobs to cut down on the amount of time a worker spends in a particular environment, and enforcing safety measures that eliminate the risk of an accident, such as a chemical spill.
While symptoms may clear up once a worker is no longer exposed to the irritant, many people find that the asthma persists and leads to the chronic airflow problems (hyperresponsiveness) typical of RADS. Further, the longer the exposure, the more chronic the asthma. Once asthma is diagnosed as being occupational in nature, it is not enough to merely open more windows or take a few more puffs on a bronchodilator. A serious discussion regarding options needs to take place between patient and doctor — away from the workplace.