In addition, in the model we have the potential for airborne contaminants to adsorb or sediment onto room surfaces and for this contamination to become resuspended in the air. A key assumption here is that the contaminant is thoroughly mixed throughout each compartment. Here the air compartments represent the local external environment, room air (where static samples are obtained), breathing zone air (where personal air samples are collected), and the inhalation of contaminants into the nose or mouth.
3 The answer must be “yes”, but perhaps a more pertinent question is: how can the relation between personal and static samples be useful in epidemiological studies or risk evaluations? A simple conceptual model, shown in fig 1, is sufficient to convince us that there must be a relation between personal and static monitoring data. Lange poses the question “are personal and static samples related?”. It is reasonable to expect that in general, personal exposure would be greater than static samples if on average workers spend a proportion of their time close to sources of the hazardous substance. The median ratio between personal and static concentrations was 1.5, although the individual data points ranged from 0.4 to 10. In this analysis more than 80% of the personal measurements exceeded the corresponding static sample concentration. This showed, as Lange asserts in his letter to this journal, 3 that personal samples are “generally higher in concentration than static samples”. 5 In this commentary, information concerning personal and static measurement results from papers published in that journal over the past 10 years was reviewed. This classic paper has recently been reproduced in the electronic edition of the Annals of Occupational Hygiene together with a commentary on its significance to the science of human exposure assessment. 4 They compared their new personal sampler with the conventional static sampler and showed that personal exposures were generally higher than those made at a fixed location. In 1957 the personal sampling pump had just been invented by Jerry Sherwood and Don Greenhalgh from the UK Atomic Energy Authority. These multimedia samples can yield as much information as several personal samples.The paper from Harrison and his co-workers 1 and the subsequent correspondence 2, 3 has reignited a debate about the relation between personal and static sample measurements that started more than 40 years ago. While these are area, not personal samples, they can be collected very close to the breathing zone of the heavy equipment operator and thus would be reasonably representative of personal exposure. Another method is to place multiple sampling devices on pieces of heavy equipment. Alternatively, if workers are in teams, a different monitoring device can be assigned to each team member. Consequently, several days may be required to measure the exposure of a specific individual using each of the media for different contaminants. Individual workers cannot typically be outfitted with more than two pumps because this can become cumbersome. Pumps should be protected with disposable coverings, such as small plastic bags, to make decontamination procedures easier.Personal monitoring may require the use of a variety of sampling media. It is best to use pumps that automatically maintain a constant flow rate to collect samples, since it is difficult to observe and adjust pumps while wearing gloves, respirators, and other personal protective equipment. These samples represent the actual inhalation exposure of workers who are not wearing respiratory protection and the potential exposure of workers who are wearing respirators. Personal monitoring samples should be collected in the breathing zone and, if workers are wearing respiratory protective equipment, outside the face piece.
If workers closest to the source are not significantly exposed, then all other workers are, presumably, also not significantly exposed and probably do not need to be monitored.Since occupational exposures are linked closely with active material handling, personal air sampling should not be necessary until site mitigation has begun. This approach is based on the rationale that the probability of significant exposure varies directly with distance from the source. those who are closest to the source of contaminant generation, is highly recommended. The selective monitoring of high-risk workers, i.e.