By Chrissy Klocker, Engineering Manager, Donaldson Company, Inc.
Hexavalent chromium has become a hot topic in the thermal spray community and among welders. Useful search terms for hexavalent chromium include "chromate" and "chrome six." New OSHA regulations are forcing everyone to take a close look at their processes and implement changes to them or install engineering controls to help reduce hexavalent chromium exposure. This paper addresses some questions regarding the new regulations, including:
- What is hexavalent chromium?
- OSHA Permissible Exposure Levels
- What industrial processes produce hexavalent chromium?
- How can a worker be exposed?
- What does hexavalent chromium do to the body?
- What are employers and employees required to do if hexavalent chromium is in the facility?
What is Hexavalent Chromium?
Hexavalent chromium shows up in predominantly three forms: 1) Trivalent Chromium, which occurs naturally as chrome ore and is also an essential nutrient for proper metabolism; 2) Metallic or Elemental Chromium, typically found in aerospace alloys; and 3) Hexavalent Chromium, typically from industrial processes like welding and thermal spray.
Hexavalent Chromium is the most toxic form of chromium.
Reading through articles and publications, you will see hexavalent chromium identified in different ways, including: Hex Chrome, Chromium (VI), Cr(VI), and Cr 6+.
OSHA Permissible Exposure Levels
The Occupational Safety & Health Administration (OSHA) has defined two levels of exposure for hexavalent chromium: a Permissible Exposure Limit (PEL) and an Action Level (AL). The current PEL for hexavalent chromium is 5 µg/m3 for a single employee over an 8-hr shift. This PEL of 5 µg/m3 was reduced from the previous standard of 52 µg/m3. A factor of 10!
The second exposure limit is called the Action Level (AL) which is currently at 2.5 µg/m3. This is the concentration of airborne Cr(VI) present in a work environment and calculated as an 8-hour time-weighted average (TWA). At either of these levels, employers are required to take specific actions, and failure to take these actions may result in penalties.
Where Does Hexavalent Chromium Come From?
There are a variety of industrial processes that can produce hexavalent chromium. Some of these include:
- Coatings (spray primers/paints)
- Coatings containing chromates: dyes, paints, inks & plastics
- Chrome plating
- Blending/sanding coatings containing chromium
- Welding and cutting of alloys containing chromium
- Stainless steel & Nickel Alloy
- Thermal Spraying, including plasma, electric arc, and combustion (including HVOF)
- Metallic chromium in the feedstock may be converted to hexavalent form.
- Hexavalent chromium may be present in a feedstock containing any form of chromium.
- Smelting of Ferro-Chromium Ore
- Portland cement impurities
- Dip-tanks
- Anodizing and Plating lines
- Leather tanning - Ammonium Dichromate
Important Clarification Points: In your facility, you may be producing a dust, fume, or mist that contains hexavalent chromium. It is important to realize hexavalent chromium has its own recommended threshold limit value (TLV) as established by the American Conference of Industrial Hygienists (ACGIH), and that this value may be lower than other components present as airborne contaminants.
Because hexavalent chromium is usually only a percentage of the dust fume and mist generated from a process, it may be worth investigating the percent contribution of Cr(VI) verse other materials in the airstream. Be advised it is entirely possible that one could exceed the TLV for hexavalent chromium while staying under the TLV for other fumes given off.
Typical particle sizes produced of the material containing hexavalent chromium differ by process and application.
| Type of Fume | Size Range of Fume Particles |
|---|---|
| Wet paints with chromates | 0.7 - 34 microns |
| Chrome plating | 0.75 - 6.4 microns |
| Welding | 0.05 - 2.0 micons* |
| Thermal Spraying | 0.05 - 2.0 microns* |
How Do Workers Become Exposed?
If your company has a process that could be producing hexavalent chromium, workers can be exposed through many sources.
- Inhalation. When exposed to processes producing dusts, fumes, or mists containing Chromium VI, you can inhale it through your nose and mouth.
- Absorption. If a medium containing hexavalent chromium comes in contact with your skin or eyes, it can be absorbed into the body.
- Ingestion. If a worker fails to use proper personal hygiene techniques when working with Cr(VI), exposed food, tobacco, and/or cosmetics can become contaminated and may be ingested.
How Does Hexavalent Chromium Affect the Body?
Once in the body, hexavalent chromium typically targets certain organs. Respiratory tract (due to inhalation damage to mucous membranes), perforation of the septum (the tissue between the nostrils of the nose), lungs, eyes, skin, liver, and kidneys are some examples.
A worker exposed to hexavalent chromium may experience symptoms such as sinus irritation, nosebleeds, ulcers (stomach and nose), skin rash, chest tightness, wheezing, and shortness of breath.
Employer Requirements
If a company has determined that it could be potentially producing hexavalent chromium, it is required to do the following:
- implement air sampling,
- medical monitoring and provide employee notification of monitoring results,
- implement engineering controls,
- adopt respiratory protection program,
- demarcation of work areas containing hexavalent chromium,
- execute an employee training program,
- provide availability of OSHA regulations and company policy to employees.
The frequency of air sampling a company must do depends on what level of hexavalent chromium was discovered in the facility. If the area is tested above the PEL of 5.0 µg/m3, testing has to be done every three months. If the area is above the action level (AL) of 2.5 µg/m3 but below the PEL, then a company is only required to do air sampling every six months. If the area is below the action level, the company is required to take an initial baseline, and then it is left up to the facility hygienists to decide on a sampling frequency. Sampling yearly is a typical strategy in this case.
Medical monitoring of all employees is required in facilities that test above the AL of 2.5 µg/m3. The standard on hexavalent chromium requires medical surveillance but leaves the selection of the specific tests to the physician or other licensed healthcare professional (PLHCP.) This may be an on-site company nurse or the employee may need to go to his own health care provider for tests.
Some of the things that a company could do include:
- Review of health and work history
- Physical exam
- Report of the outcome of the exam
Once an exam is completed, a written summary should be provided to the employee within two weeks and kept on file at the company by the industrial hygienist.
When Hexavalent Chromium is above PEL
On processes producing hexavalent chromium above the PEL of 5 µg/m3, engineering controls must be implemented. Until engineering controls are implemented, respiratory protection should be used mandatory. Please note that rotation of employees to different jobs to achieve compliance is not permitted by OSHA.
Welding and thermal spraying can produce significant hexavalent chromium emissions. The amount of hexavalent chromium in the fume may be impacted by:
- Method of welding or thermal spraying
- Electrode type or gun (welding only)
- Base metal material and composition (welding only)
- Powder or wire composition
- Voltage (higher voltages speed production but increase fume rates)
- Electrical current
- Arc length (welding only)
- Shielding gas (welding only)
- Rate of welding or thermal spraying
- Welding Angle (welding only)
When estimating how much hexavalent chromium fume is produced from a process, remember that:
- As melting rate increases, fume generation rate increases
- As the power increases, fume generation rate increases
The amount of hexavalent chromium in fume can be estimated using the following formula:
E = W x PC x EF x CF
- E = Specific metal emitted [lb/year]
- W = Total weight of electrode used [lbs/yr]
- PC = Percent composition of specific metal [%]
- EF = Emission Factor per ton of electrode [lbs/ton]
- CF = Conversion factor [1 ton or 2000 lbs]
Emission factors are expressed in a number of different ways:
- % of particulate per pound of electrode
- mg of particulates per pound (lb) of electrode
- Pound of pollutant per pound of electrode consumed
You can find emission factors from many sources* including:
You can also estimate emission factors by taking the fume generation rate and multiplying by the chrome content, then multiplying the result by the hexavalent chromium ratio:
- FGR x fume composition x % chrome as Cr6+
- (lb fume/lb electrode) x (lb Cr/lb fume) x (Cr6+/cr in fume)
Note: EF has no units = [%] x [%] x [%]
OSHA expects exposure to be reduced as far as reasonably practicable.
For work area and demarcation of areas that may contain hexavalent chromium, companies are expected to do at least the following:
- Areas with airborne exposure above the PEL must be demarcated with appropriate signage to limit unauthorized entrance.
- Locations surrounding processes using hexavalent chromium must be free of surface contamination. Of the 4 ways to clean up surface contamination (sweeping, blowing with compressed air, wet mopping, and vacuuming), wet mopping and HEPA vacuuming are the only ways that are effective and acceptable. Compressed air can only be used under very specific conditions if vacuuming is not feasible; consult the OSHA website for those conditions.
Companies are expected to make the regulations available for any employee to see.
Employee Requirements
Employees have responsibilities, too -- to protect themselves. They are required to use proper personal protective equipment, good housekeeping skills, engineering controls once implemented, and good personal hygiene techniques. Good personal hygiene includes not using tobacco, not applying cosmetics, not eating anything, not placing fingers in mouth or nose, and washing hands/face prior to doing any of the above activities, before taking a break, or at the end of their shift.
Engineering Control Should Include Good Dust & Fume Collection
A well-designed ventilation system, including a properly operated dust collector, can be a factor in reducing general hexavalent chromium exposure levels in a facility.
As shown in the chart above, the sizes of the fume particles that carry hexavalent chromium vary from 5/100 of a micron to 34 microns, and most are in the very small range (sub-micron to 2 microns). It is, therefore, necessary to use filter media in the collection system that can capture a full range of sizes, from sub-micron to large particulate. High-efficiency filters are recommended, such as Ultra-Web® fine fiber filters from Donaldson® Torit®. Each filter should have at least 1.5 inches of water gauge pressure drop across the filters to optimize performance.
A well-designed ventilation system will have sufficient capture velocities at the various hoods to help control any hexavalent chromium-containing emissions. The ACGIH Industrial Ventilation Guide offers several examples including:
- VS-90-01 through 03 for Welding
- VS-90-10 for Torch Cutting
- VS-90-20 for Robotic Welding
- VS-90-30 for Metal Spraying
- Laser tables 250 fpm for zone (not covered)
Combined with powerful Donaldson Torit Downflo® Evolution dust collectors, Easy-Trunk® or Porta-Trunk® fume collectors, a well-designed and operated ventilation system can reduce employee exposure to dusts and fumes containing hexavalent chromium.
Ambient fume collection (sometimes termed general or ambient ventilation) is not recommended, as it typically only cleans 70% of the air at any given time. The ambient collection is simply not powerful enough to take care of fumes potentially containing hexavalent chromium in the breathing zone of an employee. Capture hoods located as close to the source of generation as possible, and ducted into a well-built dust/fume collector, will ensure better confinement of the fume particles.
Your Donaldson Torit sales representative can help in determining which dust filtration products are best suited to your ventilation system design and operation. While Donaldson Torit engineers are NOT experts on Hexavalent Chromium, they know air filters and can assist you in selecting the filter suitable for your ventilation needs.
Summary
In summary, hexavalent chromium is a regulated, toxic material that must be dealt with by implementing proper precautions, including:
(a) Engineering controls where required
(b) Respiratory protection if needed
(c) Good housekeeping practices
(d) Proper personal protective equipment
(e) Good personal hygiene practices.
