The danger to spray painters of developing asthma Part 1 By Ian Davis Introduction The purpose of this article is to describe the risk of occupational lung disease caused by exposure to toluene di-isocyanate, which may be used during refinishing of vehicles undergoing repair. The second part of this article, which will be published in the next edition, will review the adequacy of various risk control measures with a view to recommending realistic pragmatic improvements where necessary.
Background It has been reported that isocyanates are the leading cause of occupational asthma in the Western World, accounting for 9-15% of new cases of asthma in adults of working age. Spray painters are considered to be a particularly vulnerable grouping due to the use of Isocyanate based paints, which are known respiratory sensitisers; the causal agents responsible for developing asthma; the UK’s Health and Safety Executive claim that vehicle paint sprayers are 80 times more likely to develop this condition than a general worker.
takes place in the body. TDI has been assigned a Occupational Exposure Level (OEL) value and has an identifying sensitizing “Sen” notation under the Health and Safety Authority’s 2010 code of practice for the Safety Health and Welfare at Work (Chemical Agents) Regulations 2001.
Sensitization Occupational asthma creates a state of immunological hypersensitivity in the lungs that results in the formation of excessive or disproportionate amounts of anti-bodies to fight off the inhaled foreign substances (i.e. antigen). During an asthmatic attack, the antigen-antibody reaction ultimately produces histamine, an inflammatory agent that causes the constriction of smooth muscle, inflammation of the airway wall and thickening of the mucus layer. Combined, these effects narrow the conducting airways and restrict the flow of air reaching the alveoli (see figures below, disrupting the body’s natural balance.
Rehabilitation Whilst the effects are localized, this is a debilitating condition that dramatically and adversely affects a person’s quality of life. Once sensitized, even a tiny amount of exposure to isocyanate, even well below occupational exposure limit value, could trigger an attack in a person. Such a physical condition would almost certainly mean the sprayer would need to be re-assigned to safer alternative duties. If exposure to TDI, the causative agent, ceases completely, the condition will nearly always improve. If this happens within the first two years of the development of the condition then complete recovery is usual.
During spraying the sprayer is exposed on a daily basis to inhalation of TDI during the painting episodes and until the ‘clearance time” for extracting vapours has expired. The operative is also exposed during the cleaning of his spray gun using compressed air, which takes place inside the booth and lasts a few minutes.
In this theoretical scenario spray painting is carried out in a purpose built “SAICO” spray booth equipped with an integrated computer-controlled “downdraft” mechanical ventilation system with set air exchange rates, which operates under negative air pressure to prevent paint mist leaking out. Spray painting is carried out using a “traditional” hand-held spray gun using water based paints, which contain TDI hardners.
Isocyanate based paints are known respiratory sensitizers that target the lungs, resulting in chronic reversible obstructive airway disease, more commonly known as occupational asthma. The vapour damages the lower respiratory tract, specifically the alveoli where the exchange of oxygen and carbon dioxide
The duration of attacks usually varies from a few minutes to hours (status asthmaticus). In severe acute attacks it may prove fatal although these circumstances happen very rarely.
Assessing the risk
The exposure
The paint spray gun creates a fine paint mist that envelope the operator. The mist isn’t extracted instantly, the “clearance time” for removing the paint mist takes 5-minutes due to the velocity and flow rate of the spray gun air jet. The severity of the exposure can be under-appreciated due to the fact that the fine” paint mist is tasteless, odourless and largely undetectable under normal lighting.
• Breathlessness; and shivers. • Flu-like
Conclusion The sensitisation process does not occur after one exposure but develops over time (i.e., latency period). Latency periods are variable and can be as short as several weeks or as long as 30 years. The risk of development of sensitisation is usually dose related, that is the higher the exposure the more likely the individual will become sensitised.
What are the symptoms of occupational asthma? Typical early signs of respiratory sensitization to isocyanate include one or more of the following: tightness; • Chest Persistent cough; • • Persistent cold; • Wheezing;
Spray painting using isocyanate paint is a high-risk occupation. Consequently the health surveillance methods aimed at providing medically conclusive evidence of the body’s level of exposure to isocyanates is critical together with comprehensive and robust risk control measures. The second and concluding part of this article will discuss ways of managing the risk and discussing the various methods of determining the sprayers exposure. The guidance in this article was drawn from literature published by the Health and Safety Authority and the UK’s Health and Safety Executive.
53