1.1 Considering the workload
Exposure standards are set on a time period of eight-hour exposure during normal work intensity, normal climatic standards and a sixteen-hour gap between the working shifts to allow the eradication of absorbed chemicals.
The conditions to which a worker is exposed can play an important role in the absorption of chemicals and can worsen the health risks. A person who performs more physical activities at work will tend to breathe more heavily and absorb more chemicals. Other factors can increase the risk of a worker such as his heart rate, respiration rate, diet and whether he is a smoker or not. These factors should be taken into consideration as well.
1.2 Skin absorption
Chemicals like aniline, nitrobenzene, phenols and some pesticides can quickly penetrate the skin and be absorbed in the body. Sometimes, this absorption through skin can prove to be more dangerous compared to inhalation. Dermal absorption can occur through a splash onto skin or the apparel or at times even through exposure to high concentrations of fume or vapour and therefore special procedures need to be taken to prevent skin contact.
Biological monitoring can be used to investigate the amount of chemical uptake when skin absorption is significant.
1.3 Exposure to multiple substances – Independent effect and additive effects
Normally, exposure standard is applicable to airborne concentrations of a single pure substance however in the real world, a worker maybe exposed to many different chemicals in the workplace. This could happen at the same time altogether or at different times and it can increase the health risk. Interaction of a mixture of contaminants should be scrutinized by toxicologists as well as occupational hygienists.
- Independent effects occur when two or more substances have completely different effects on the body. Each chemical can be assessed separately against the exposure standard.
- Additive effects occur when two or more chemicals target the same organ in the body or the same mechanism of action and have a combined effect altogether. The resultant aggregate effect is measured against the exposure standard. When assessing a mixture, it is important to identify and quantify all chemicals.
- Synergism occurs when two or more chemicals each have an individual effect but the combined effects is greater than the additive effects.
- Potentiation occurs when a single chemical or a mixture amplify the effect of another substance or mixture.
1.4 Odour thresholds
The absence of an odour may not necessarily imply a safe workplace; conversely, the presence of an odour may not imply a risk to health and safety. An odour threshold perception can vary from individual to individual over the different magnitudes and the different substances. The presence or absence of an odour may not have any link to its biological effects. An interference from other chemicals is also possible.
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