The Power and Utility of Mathematical Models

The phone rings and you answer. On the other end of the line is a clinician from a healthcare provider for an employee who has a set of symptoms. To help with their diagnosis, the clinician asks you to tell her about the worker’s chemical exposures. The employee works with solvents, and you have a list of chemicals used in the department where the employee works. You also have air sampling data for some chemicals in some work areas but not for other chemicals in other areas. And the concentration measurements you have aren’t comprehensive. What sort of information can you give the clinician about exposure levels?

You get a report of a worker feeling sick after a chemical exposure. She had opened an unventilated storage closet and encountered the strong smell of an organic vapor. A metal container containing Stoddard solvent had developed a leak about halfway down the side of the container. The worker suffered from a strong headache but soon felt better. Even though the situation seems to be resolved, you still want to document what sort of exposure she had. How can you get a handle on that?

The purchasing department, with input from both the production department and employee representatives, comes to you with a product recommendation. The product reportedly works better and is less expensive than the one currently used, but it contains methylene chloride. You know methylene chloride triggers exposure assessment requirements. How do you respond to the product recommendation?

These are just a few examples of many scenarios where industrial hygienists have to make decisions about exposures with limited information available to support their judgment. It’s part of the job of industrial hygienists to know about the exposures occurring at their facilities. But fully understanding them all is a monumental task.

In a world of limited budget, time, and personnel, success can hinge on the ability to leverage resources. And one of the major goals in the world of industrial hygiene is to characterize the level of risk to which workers are exposed in the course of the myriad tasks they perform. Even though the list of chemical exposures at a small facility may be short, the industrial hygiene assets for such a facility are often short as well. Larger facilities tend to have more industrial hygiene resources, but they also use more chemicals and their workers perform more tasks. In their efforts to get a firm handle on all of the exposures that need to be anticipated, recognized, evaluated, and controlled, many industrial hygienists constantly feel one or more steps behind.
Disadvantages of being unacclimatized:
  • Readily show signs of heat stress when exposed to hot environments.
  • Difficulty replacing all of the water lost in sweat.
  • Failure to replace the water lost will slow or prevent acclimatization.
Benefits of acclimatization:
  • Increased sweating efficiency (earlier onset of sweating, greater sweat production, and reduced electrolyte loss in sweat).
  • Stabilization of the circulation.
  • Work is performed with lower core temperature and heart rate.
  • Increased skin blood flow at a given core temperature.
Acclimatization plan:
  • Gradually increase exposure time in hot environmental conditions over a period of 7 to 14 days.
  • For new workers, the schedule should be no more than 20% of the usual duration of work in the hot environment on day 1 and a no more than 20% increase on each additional day.
  • For workers who have had previous experience with the job, the acclimatization regimen should be no more than 50% of the usual duration of work in the hot environment on day 1, 60% on day 2, 80% on day 3, and 100% on day 4.
  • The time required for non–physically fit individuals to develop acclimatization is about 50% greater than for the physically fit.
Level of acclimatization:
  • Relative to the initial level of physical fitness and the total heat stress experienced by the individual.
Maintaining acclimatization:
  • Can be maintained for a few days of non-heat exposure.
  • Absence from work in the heat for a week or more results in a significant loss in the beneficial adaptations leading to an increase likelihood of acute dehydration, illness, or fatigue.
  • Can be regained in 2 to 3 days upon return to a hot job.
  • Appears to be better maintained by those who are physically fit.
  • Seasonal shifts in temperatures may result in difficulties.
  • Working in hot, humid environments provides adaptive benefits that also apply in hot, desert environments, and vice versa.
  • Air conditioning will not affect acclimatization.
Acclimatization in Workers