Controls in Industrial Environments
The OEHS Professional’s Role, Part 2
BY D. JEFF BURTON
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Historically, most life- and health-threatening employee exposures to airborne hazards have occurred in industrial environments. This article explains the controls typically used in these environments and offers examples of each.
As a recap, part 1, published in the May 2021 Synergist, discussed the importance of determining and applying appropriate emission and exposure controls. This is one of an OEHS professional’s main responsibilities. Controls typically fall into three general categories: administrative controls, personal protective equipment, and engineering controls. The latter include process and equipment changes, substitution, isolation, ventilation, source modification, and other approaches. The types of control we choose are largely determined by:
• Regulatory requirements. Some operations require specific controls; for example, lab ventilation requirements are included in OSHA’s standard on Occupational Exposure to Hazardous Chemicals in Laboratories (29 CFR 1910.1450).
• The nature of the hazard. For example, a chemical hazard will have different controls than a physical or biological hazard.
• The way the hazard affects the employee. For chemical hazards, the route of entry into the body helps determine the appropriate controls.
• The technical feasibility of potential controls.
• Costs.
OEHS professionals usually make the following assumptions about controls:
1. All hazards can be controlled to some degree and by some method.
2. There are usually alternative approaches to control a hazard.
3. More than one control is often useful or required.
4. Some control methods are more technically feasible than others.
5. Some are more cost-effective than others.
6. The controls we initially apply may not completely control the hazard, so we need to be prepared to add to our control strategies.
7. Processes, equipment, and personnel may change over time, so again, we need to monitor the situation and make changes as necessary.
Traditionally, employees have been divided into two categories: white-collar workers who work in commercial establishments like stores and warehouses or in office, classroom, and medical environments; and blue-collar workers who are employed at various industrial and production facilities, chemical and biological laboratories, and mines, smelters, and foundries. Part 1 covered the controls often found in white-collar work environments. This article covers industrial controls used to protect blue-collar workers.
SUBSTITUTION WITH A LESS HAZARDOUS MATERIAL
When feasible, substituting a highly toxic chemical emitter with a less toxic one is generally the best approach to control. Substitution can come close to the ideal of eliminating the hazard. Many toxic materials have suitable substitutes with lower toxicity ratings or rates of evaporation or emission. Historical examples are legion: walnut shells for sand in blasting, hydrochlorofluorocarbons for fluorinated or chlorinated hydrocarbons in solvents, toluene for benzene in paint thinners, titanium dioxide for white lead in paint, and so forth.
When substituting with a less toxic material, always consider the potential resulting problems. For example, acetone is less toxic than toluene, but it may increase emissions due to its lower boiling point and increase the fire hazard due to its lower flash point.
Sometimes a material’s properties can be modified to reduce emissions. Examples of these modifications include lowering the temperature of a solvent to reduce evaporation and wetting or pelletizing dusty materials to reduce pulvation—that is, the emission of particles into the air.
PROCESS AND EQUIPMENT CHANGES
A process change, like substitution, attempts to replace more hazardous equipment or processes with less hazardous equipment or processes. Historical examples of process changes include paint dipping for paint spraying, polyester resin adhesives for lead solder in metal seams, low-speed oscillating grinders for high-speed rotary grinders, bolting for welding, cooling-coil vapor degreasing tanks for hand washing of parts, continuous closed processes for open batch processes, and so forth.
Again, we should evaluate the proposed change on the basis of the hazards it creates and its effects on productivity and product quality. Fortunately, process or equipment changes used for hazard control often result in increased productivity and improved product quality.
ISOLATION AND ENCLOSURE The principle of isolation is applied in almost every industrial site. Implementations may be as simple as erecting a wall between a process and the employee (for example, separating workers from production equipment) or as complicated as establishing automated processes using robotic techniques (such as those used for remote spray painting of automobile body frames). Enclosures, closely related to isolation, usually take the form of building an airtight structure around the process or the employee.
Isolation and enclosure take many forms in industrial operations. Enclosures are built around dusty materials, sandblasting operations, chemical operations, hazardous chemicals, and crane operators, who are typically enclosed in air-supplied cabs. Other examples include consolidating chemical pipes and lines into an enclosed area, moving materials through pneumatic conveyance instead of using an open conveyor belt, and enclosing and exhausting sampling and view ports.
Isolation includes separation by time as well as space. For example, foundry shakeout can be scheduled during the evening when most employees have left the workplace or maintenance can be performed during regular shutdown periods when production employees are not present.
VENTILATION Ventilation is a universally used and time-tested approach to emission and exposure control. Every laboratory and industrial facility employs some type of ventilation to promote or protect the health of workers.
The general control category of ventilation includes a number of approaches, which are defined in Table 1. The resources listed at the end of this article cover these approaches in more depth.
Again, we should evaluate the proposed change on the basis of the hazards it creates and its effects on productivity and product quality. Fortunately, process or equipment changes used for hazard control often result in increased productivity and improved product quality.
ISOLATION AND ENCLOSURE The principle of isolation is applied in almost every industrial site. Implementations may be as simple as erecting a wall between a process and the employee (for example, separating workers from production equipment) or as complicated as establishing automated processes using robotic techniques (such as those used for remote spray painting of automobile body frames). Enclosures, closely related to isolation, usually take the form of building an airtight structure around the process or the employee.
Isolation and enclosure take many forms in industrial operations. Enclosures are built around dusty materials, sandblasting operations, chemical operations, hazardous chemicals, and crane operators, who are typically enclosed in air-supplied cabs. Other examples include consolidating chemical pipes and lines into an enclosed area, moving materials through pneumatic conveyance instead of using an open conveyor belt, and enclosing and exhausting sampling and view ports.
Isolation includes separation by time as well as space. For example, foundry shakeout can be scheduled during the evening when most employees have left the workplace or maintenance can be performed during regular shutdown periods when production employees are not present.
VENTILATION Ventilation is a universally used and time-tested approach to emission and exposure control. Every laboratory and industrial facility employs some type of ventilation to promote or protect the health of workers.
The general control category of ventilation includes a number of approaches, which are defined in Table 1. The resources listed at the end of this article cover these approaches in more depth.
Table 1. Types of Industrial Ventilation
WET METHODS
Wetting a dusty material can reduce particle pulvation, but it must be compatible with the process. Adding humidity to a material is sometimes effective because it may create agglomeration among small particles and add weight. Examples of wetting include fogging sprays at conveyor belt transfer points, water washing of dusty surfaces, wetting of sand in sandblasting, and adding humidity to dry air to reduce IAQ complaints.
ADMINISTRATIVE CONTROLS
Traditional administrative controls include rotating employees to reduce exposure times, instituting emission- or exposure-reducing work practices, developing preventive maintenance programs, instituting good housekeeping programs, training and educating employees, conducting medical exams, and teaching and requiring good personal hygiene. Another, less common administrative control is to completely eliminate the process or hazard by subcontracting the work to some other entity that has appropriate emission and exposure controls. Some of these options are discussed in more detail below.
But first, it should be noted that engineering controls that eliminate or reduce the emission hazard are generally preferable to administrative or PPE controls. Some administrative controls typically place at least part of the burden of responsibility for health protection on the worker. However, administrative controls are often effectively used in conjunction with, or in addition to, engineering controls. Indeed, very few airborne hazards are controlled by one control measure alone, and some types of administrative controls—for example, training and education—are almost always required.
A successful control strategy of a welding operation, for example, might include local exhaust ventilation (which automatically provides some dilution ventilation as well), use of a less toxic welding rod material, good housekeeping of the welding area to prevent secondary emissions of dust, preventive maintenance of welding equipment, use of respirators and other PPE, and training and educating the welders so they can work with minimum emissions and exposures. Simple adjustments of head position can have an impact on exposure concentrations.
Good Housekeeping
Emitted particulate materials must go somewhere. If they don’t go out the stack or the window, they settle on horizontal surfaces in the plant. Settled materials can become secondary emission sources, often with as much or more impact on exposures as the primary source. For example, sweeping—while a small source compared to, say, a vibratory conveyor—can be a significant source of exposure because the breathing zone of the sweeper is only a few feet away from the emission point. All buildings vibrate, and such vibration can be the energy source—along with wind and traffic—to pulvate dust into the air.
Some OSHA standards, such as the standard for inorganic lead, require good housekeeping. All guidelines for good practice mention housekeeping as an important control. Dust may be removed and controlled by wet cleaning methods and vacuum systems. Sweeping and blowing can create unwanted emissions and should sometimes be avoided. Spilled liquids should be cleaned up before evaporation causes a problem. Rags and absorbent materials should be disposed of following local fire and hazardous waste requirements.
Personal Hygiene
Personal hygiene is important to the overall protection of the worker but can also impact the inhalation exposure. For example, if a worker smokes without washing his or her hands, hazardous chemicals may be inhaled through contaminated cigarettes. Similarly, if dirty clothes are taken home, additional exposure may result during clothes handling and washing.
Preventive Maintenance
Preventive maintenance of emission controls can minimize the potential for increased emissions over time. Without preventive maintenance, for example, a container seal could fail after three months of use, increasing fugitive emissions. Preventive maintenance attempts to repair, replace, or correct potential deficiencies before the problem occurs.
All emissions—whether planned or unplanned, continuous or intermittent—are impacted by the quality of maintenance applied to the process or equipment that is emitting contaminants. Insufficient maintenance increases the likelihood of both catastrophic emissions (for example, the rupture of a pipe flange) and fugitive emissions (such as slowly increasing rates of leaks from flanges, seals, joints, and access doors). Poor maintenance may increase emissions when normal emission controls are detached or impaired—for example, during filter replacement or equipment repairs. Note also that maintenance itself may lead to elevated emissions in the vicinity of maintenance personnel. In these cases, training and PPE should be provided to minimize exposures to maintenance personnel.
PPE AND RESPIRATORS
Appropriate PPE and respirators are often used to protect employees from exposures. Gloves, for example, can help protect against contaminating the hands. Respirators, while protecting against inhalation hazards, should not routinely be substituted for available engineering and administrative controls because doing so does not reduce the airborne hazard in the workplace, which is the preferred approach; it tends to place the responsibility of protection on the worker; and it could be in violation of OSHA standards. The generally accepted occasions when respirators are used include during maintenance and repair work, when other controls are not feasible, during the time other control measures are being installed or instituted, during emergencies, and when they are used to supplement engineering and administrative controls that fall short of providing needed protections.
CHOOSING APPROPRIATE CONTROLS
Once we have identified all potential emission and exposure control methods available to us, how do we determine which ones to apply or use? NIOSH has traditionally defined five levels in a general hierarchy of controls, listed in this preferred order of application: elimination, substitution, engineering controls, administrative controls, and personal protective equipment. But we should also take into account a potential control’s effect on production and cost, as well as employee acceptance of the control. The sidebar below presents a case study on selecting controls.
A typical approach is to determine and list all potential controls, arrange them in order as suggested by NIOSH, look at the costs and details of implementation, investigate the effectiveness of controls in similar situations elsewhere (if available, for example, in another plant with similar operations), and then select those that are most cost-effective for your unique situation. The final selection of appropriate controls is sometimes difficult and usually requires the input of everyone concerned: the OEHS professional, management, employees, accountants, and others.
D. JEFF BURTON, MS, PE, FAIHA (former CIH and CSP, VS), is an industrial hygiene engineer with broad experience in ventilation used for emission and exposure control.
Acknowledgement: The author thanks Jeff Throckmorton for reviewing and providing helpful comments on this article.
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CASE STUDY
In a food production plant’s chemical laboratory, lab workers have been complaining about the smell of solvents in the air. Routine air samples taken in the breathing zones of those complaining shows exposures to toluene at concentrations below the PEL, but any exposures should be understood and controlled to the extent possible. The OEHS department investigates further and determines that two lab technicians are using toluene to clean some food production equipment on an open lab bench. While most equipment is cleaned inside a lab fume hood, some of the equipment is too big to fit inside the hood.
The OEHS professional makes a list for management of the potential emission and exposure controls that could be applied:
1. Newer food processing equipment could be purchased that does not require periodic cleaning, which would eliminate the current emissions and exposures.
2. A larger laboratory fume hood could be purchased that would fit all the equipment needing to be cleaned.
3. The cleaning compound could be changed to less toxic chemicals such as xylene.
4. Parts cleaning might be performed using soap and water or other non-toxic cleaning compounds.
5. The food production equipment cleaning could be subcontracted to an outside cleaning company.
6. The general exhaust ventilation in the space could be increased, thus reducing average concentrations in air.
7. The cleaning operation could be rotated among all seven lab employees so that average personal exposures would be reduced.
8. Lab technicians who perform the cleaning could be equipped with respirators until better controls can be implemented.
9. The food production equipment manufacturer and supplier could be contacted to see what they recommend.
The OEHS professional also provides rough estimates of the costs of implementing each item. Management, after reviewing the proposals and their approximate implementation costs, decides to implement items 3, 4, 7, 8, and 9 until item 2 can be completed in about four weeks.
RESOURCES
AIHA: Industrial Hygiene Workbook, 6th ed., chapters 11–22 (July 2016).
AIHA: The Occupational Environment: Its Evaluation, Control and Management, 3rd ed., sections 2, 6, and 7 (October 2016).
National Safety Council: Fundamentals of Industrial Hygiene, 6th ed. (2012).
Wiley: Patty’s Industrial Hygiene, 7th ed., vol. 2, parts 4 and 7 (2021).