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Occupational Asthma

Contents

1. What is occupational asthma?
2. What are the symptoms and signs of occupational asthma?
3. What health assessment is required?
4. What preventative measures can be taken in the workplace?

1. What is occupational asthma?

Asthma is a condition of the lungs whereby the airways to the lung narrow and cause symptoms of coughing, shortness of breath, wheezing and chest tightness.

The exact cause is unknown but it is often made worse or triggered by a number of factors in the person's environment.

When asthma occurs as a result of exposure to airborne substances in workplaces, it can be divided into two categories:

• asthmatic symptoms induced in workers with pre-existing asthma by non-specific respiratory irritation; and
• an asthmatic syndrome caused by hypersensitivity to a specific agent (sensitising agent) in the work environment in a previously non-asthmatic person.

The term OCCUPATIONAL ASTHMA should be confined to the hypersensitivity syndrome, which has a very different course and prognosis from that of non-specific irritation.

2. What are the symptoms and signs of occupational asthma?

Occupational asthma occurring in response to regular exposure to a sensitising agent in the workplace usually exhibits certain characteristic features.

• there is always a latent period of several weeks to many years, during which the worker is free of symptoms;
• recurrent "runny nose and eyes"  during working hours is common at the beginning;
• this is followed after a variable period by the development of coughing, wheezing, chest tightness and shortness of breath which increases in frequency and severity until a pattern of repeated sickness absence is established; and
• coughing is often the most prominent symptom, and may completely overshadow difficulty in breathing or chest tightness.

Sometimes the worker complains of symptoms within a few minutes to an hour of exposure to the sensitising agent. More often, symptoms do not develop for 4-8 hours after the start of the workshift, and increase in severity after the end of the shift. This means that many workers develop disabling symptoms in the afternoon on their way home, or later in the evening and may not relate them to exposure in the workplace.

A significant proportion of workers are free of symptoms during their working hours, suffering only night-time attacks that wake them in the early hours of the morning. It is this group in which the occupational cause is most frequently overlooked.

In the early stages:

• symptoms are least on the first working day but increase progressively during the week, reaching a peak on the last day; and
• gradually resolve over the weekend.

If the occupational cause of the asthma is not recognised, or if the worker perseveres with the job despite the symptoms, there is a significant risk that the asthma will persist for years (if not indefinitely) after eventually leaving the job. The asthma will then be indistinguishable from that occurring in the general population, and may even take on allergic features with reactions to common environmental allergens such as house dust.

3. What health assessment is required?

 Pre-placement and Periodic Medical Assessment

It is not yet possible to positively identify individuals who will become sensitised. However, there are indicators which can assist in identifying those at greatest risk.

The medical and occupational histories of new workers are vital in this regard. Details of previous workplace exposure, allergies, and respiratory and dermatological disorders should be obtained.

The only justifiable reason for declaring a worker, on grounds of sensitisation, as permanently unfit to work with a sensitising agent, is a clear history of sensitisation to the sensitising agent with which they will be working. 

Close attention and careful appraisal should be given to workers who have conditions that may increase their sensitivity to the irritative effects of a substance. These include conditions such as:

• asthma;
• chronic bronchitis;
• emphysema;
• bronchiectasis;  and
• allergic skin conditions.

When doubt exists as to whether a worker with one of these conditions should risk exposure to a sensitising agent, consultation should be sought with the worker's personal physician or specialist managing the disorder.

The initial physical examination to identify individuals at greater than normal risk and to obtain baseline information should include at least the following components:

• examination of the skin for signs of dermatitis;
• clinical examination of the lungs for disorders of any kind; and
• pulmonary function testing for FEV1 and FVC.

It is vital that the worker be informed of risks to his/her health that may result from exposure to a sensitising agent. He/she should be told of the early symptoms of sensitisation and advised to report them to a doctor if they appear.

Periodical Medical Assessments

Regular assessments of workers who are exposed to sensitising agents are recommended. There is no standard for the frequency of these periodic examinations, but it is recommended that where a worker has no pre-disposing health problems he/she be seen six months after starting work and then once a year. For those at greater risk, consideration may be given to examining more frequently.

At such periodic assessments the exposure history should be updated and a functional inquiry should be made with specific reference to the following symptoms:

• irritation of eyes, nose and throat;
• coughing, dyspnoea, wheezing, chest tightness at work and at home; and
• skin changes.

At what workplaces am I at risk of developing occupational asthma? The following table outlines some of the more common occupations which involve the use of sensitising agents:

This list is not all-inclusive. The Occupational Safety and Health Act 1984 requires employers to provide, where practicable, a working environment in which employees are not exposed to hazards (section 19). The Occupational Safety and Health Regulations 1996 require employers to identify hazards from oxygen deficient or toxic atmospheres; assess the risk of harm or injury; and consider means to reducethe risk (Part 3, Division 3).

4. What preventative measures can be taken in the workplace?

1. Subsitution

Replace the hazardous substance with a non-hazardous, or less hazardous, substance, where possible.

2. Engineering and ventilation

If substitution is not possible, reduce the risk by removing hazardous substance to a safe area, enclosing the work using the hazardous substance in a confined environment, and install ventilation and exhaust systems.

The Occupational Safety and Health Regulations 1996 require employers to consider reducing the risk of exposure to oxygen deficient or toxic atmosphere by:

• using an effective ventilation system
• providing an exhaust system to extract contaminants
• other means.

3. Respiratory protection

If no other form of control is effective, use personal protection to reduce the risk to employees. The Occupational Safety and Health Regulations require employers, main contractors and self-employed persons to ensure that each person who may be exposed to toxic atmosphere is provided with respiratory protective equipment, selected, used and maintained in accordance with AS/NZS 1715, to suit the circumstances of each case. The equipment must comply with AS/NZS 1716 and must be readily available. 

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