Occupational asthma

Asthma is a condition of the lungs where 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. 

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 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 has 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. 

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 irritant 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. 

What work or substances may present an occupational asthma risk?

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, as far as 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 toxic atmospheres; assess the risk of harm or injury; and consider means to reduce the risk (Part 3, Division 3). 

Common occupations which involve the use of sensitising agents
Occupation Substance

Cabinet makers and joinery workers

 Wood dust (some species)

Welders and metal workers  

Oxides of nitrogen; nickel; chromium, cobalt

Spraypainters, boat builders and construction workers

Curing agents for epoxy paints and resins
Isocyanates in 2-pack paints

Polyurethane foam manufacturers

Toluene di-isocyanate (TDI), other isocyanates

Silo workers and grain handlers

Cereal grains; grain mites

Aluminium smelter (pot room) workers

Aluminium smelting fumes 

Food manufacturing

Egg, fish or crustacean proteins, castor bean dust, soy bean dust, coffee bean dust, flour dust, papain (enzyme), carmine

Chemical industry workers, plastic manufacturers

Phthalic anhydride, tetrachlorophthalic anhydride or maleic anhydride
Isocyanates
​Latex
Diazonium salts
Trimellitic anhydride
Ethylenediamine
Azodicarbonamide
Subtilisins (enzymes)

Hairdressers 

Henna, latex, persulfates

Health care workers

Latex, glutaraldehyde, chloramine-T

Solderers 

Colophony; rosin based fluxes 

Pharmaceutical manufacturers

Carmine; enzymes, opiates, penicillins, cephalosporins, spiramycin, piperazine

Animal house workers, laboratory workers and stable hands

Animal proteins, animal excreta

 

What preventative measures can be taken in the workplace? 

Substitution

Replace the hazardous substance with a non-hazardous, or less hazardous, substance, where possible. Eg replace powdered latex gloves with non-powdered latex gloves or nitrile gloves. 

Engineering and ventilation 

If substitution is not possible, reduce the risk by removing hazardous substance to a safe area, enclosing the process, or installing ventilation and exhaust systems. 

Administrative controls 

Develop and implement safe work practices, for example practices that reduce the amount of the substance released to the atmosphere.

Personal protective equipment  

If no other form of control is sufficiently effective, use personal protective equipment (PPE) to reduce the risk to employees. PPE should be selected with regard to the relevant Australian/New Zealand Standards. Employees must be trained in the correct use, care, maintenance and storage of PPE.  

Information and training  

Staff should be provided with information and training in relation to workplace hazards, including substances that can cause occupational asthma. Information and training should cover:

  • which substances may present an occupational asthma risk;
  • asthma symptoms and the likelihood that asthma (once developed) may be permanent;
  • procedures for reporting symptoms and the need to report symptoms promptly;
  • correct use of control measures (including PPE);
  • work practices that may reduce the risk; and
  • emergency procedures.  

Health surveillance and medical assessments

Health surveillance is required for certain hazardous substances, such as isocyanates and inorganic chromium. For information on medical assessments for other substances that can cause occupational asthma, refer to section 3 above. 

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