Controlling Occupational Exposures
The role of an industrial hygienist is to recognize potential exposure hazards, evaluate exposures, provide input for the development of controls, and finally evaluate control methods for effectiveness in reducing exposures.
When controls are warranted, the process begins with a risk assessment to characterize the problem. The hygienist can provide assistance in identifying and characterizing the hazard, the emissions and sources, worker involvement with the sources and how air movement occurs.
Control measures can be grouped into three categories: administrative, engineered, and personal protective equipment. When considering controls, there are five fundamental assumptions to bear in mind:
All hazards can be controlled (to some degree).
There are different approaches for control.
Sometimes, more than one control method is needed.
Some control methods are more cost-effective than others.
Controls may not always be completely effective in limiting the exposure hazard.
Administrative controls place part of the burden of control on the worker and are often not completely effective when used as a single approach. Examples of administrative controls include rotating workers, providing best practice training for performing job tasks, improving personal hygiene, and implementing housekeeping programs.
When considering options, it is necessary to evaluate the sources of exposure, the way in which it can affect the worker, and the route of entry. Typical routes may include unprotected exposure to noise, skin contact or inhalation of vapors and aerosols. The controls considered should be matched with the employee, the process or task, and be cost-effective. In some cases, there are regulatory requirements for controls such as the OSHA (Occupational Safety and Health Administration) requirement for exhaust ventilation for abrasive blasting (1910.94).
Worker rotation is frequently used to reduce the amount of time a worker is exposed to a hazard. A common example is rotating workers performing jobs in high-noise areas. Another example is to move workers every few hours who perform highly repetitive job tasks to reduce musculoskeletal strain.
Training in good work practices can significantly reduce exposures. For example, coaching proper body postures such as how to stand and position the head while welding or reinforcing the need to face forward to work and pivot feet instead of twisting the body.
Good housekeeping and personal hygiene are also important components of administratively controlling exposures. Settled dust becomes a secondary source of exposure with increased air movement, traffic activity and vibration produced by equipment. Frequent cleaning helps to prevent dust accumulating on surfaces.
Training and reinforcing the need for personal hygiene, such as frequently washing hands and avoiding hand to mouth contact while working can reduce the risk of exposure by ingestion. Several standards contained in OSHA 1910 Subpart Z for toxic and hazardous substances mandate personal hygiene practices. Administrative controls are usually used in conjunction with engineered controls.
Although they are more expensive to implement, engineered controls are the most effective since they offer greater cost savings over time. Examples of engineered controls include source modification, substitution, process change, isolation, and ventilation. The development and installation of engineering controls is usually the responsibility of a facilities engineering department and maintenance staff.
Source modification refers to changing an emission source to make it less hazardous. An example of source modification is wetting dust particles released in a foundry shakeout operation to reduce dispersion. Another example may be to reduce temperatures to lower the level of chemical off-gassing and vaporization.
Modifying a process to reduce the hazard is another type of engineered control. An example of this would be to dip rather than to spray paint parts. Automation would also be an example of changing the process. A good example is robotic welding to replace manual welding.
Substitution refers to changing to a different material, type of equipment, or process to reduce the hazard. Examples include substituting a solvent having a low occupational exposure limit (OEL) and higher vapor pressure to a different solvent having no established OEL, or a lower OEL and less volatility.
Isolation refers to separating employees from hazardous processes, equipment, or environments. Isolation can be achieved by placing barriers around equipment or materials, such as the use of ventilated flammable cabinets or placing enclosures around high-noise sources. Isolation separates employees from hazards. Examples are control rooms, isolation booths and supplied air islands.
Ventilation is frequently used as a method to control emissions near the source or to dilute emissions to levels that are acceptable. Local exhaust ventilation (LEV) attempts to eliminate emissions to the work room air. LEV controls are designed to capture, control, or eliminate emissions using control structures such as hoods, exhausted enclosures, ductwork, air cleaners, fans, and exhaust stacks.
General exhaust ventilation relies on fresh air dilution, either by open doors, windows or make-up air provided by air intakes and ventilation systems. For constant emission sources, effective dilution relies on good air mixing and constant air flow.
In addition to engineered solutions, regular and preventative maintenance is an important part of preventing uncontrolled and unexpected exposures. Insufficient maintenance could result in a catastrophic failure such as a rupture failure, increasing leaks from flanges, seals, access doors, and breakdowns of equipment.
Personal protective equipment (PPE) should always be used as the last option for control when other methods of control are not feasible or effective enough to reduce exposure to safe levels. Relying solely on earplugs or respirators places the burden of control on the worker and the protection is only as good as how properly the PPE is fit, worn, and maintained.
There are many different options to help keep workers safety, contact us to evaluate exposure concerns in your facility.
Mary Dunlap is a Certified Industrial Hygienist and has been with Cornerstone Environmental, Health and Safety since 2016. When she is not working, you can find Mary enjoying the outdoors.
Source: Case Studies: Sixty Practical Approaches of OH&S Control Principals. D. Jeff Burton, MS, PE (former CIH (Certified Industrial Hygienist), CSP)
