Hazards are ever-present in the steel plant environment, and a heightened awareness and emphasis on safety is a necessary priority for
our industry. This monthly column, written by members of the AIST Safety & Health Technology Committee, focuses on procedures and
practices to promote a safe working environment for everyone.
What the Hex Is With Chromium?
Summary of Initial Exposure Determinations in the Steel Industry
and Approaches to Reduce Exposure
Hexavalent chromium, sometimes referred to as
“Chrome Six,” “Cr+6” or “Cr (VI),” is a hazardous form of
the element chromium that is rarely found in nature and is
generally man-made. Hexavalent chromium is widely used
in pigments, metal finishing (electroplating), wood preservatives and fungicides, anti-corrosion paints/coatings, and
in chemical synthesis as an ingredient and/or catalyst.
Hexavalent chromium may also be present in fumes generated during the production or welding/torch cutting of
chrome alloys. Chromium metal is often alloyed with other
metals or plated on metal and plastic substrates to improve
corrosion resistance and provide protective coatings. The
steel industry is a major consumer of chromium metal in
the production of stainless steel or high-grade chromium
alloys. Stainless steel and high-grade chromium alloys do
not contain hexavalent chromium; instead, chromium is in
a zero state, and chromium in the +3 valence may be present on the surface. Extreme temperatures applied to the
chromium may result in the formation of Cr+6 as part of
the total fume produced. In addition to the melting/manufacturing of stainless steel and chromium alloys, other
operations or processes in the steel industry with potential
for hexavalent chromium exposures are: tin plating lines,
electrogalvanizing lines, hot-dip zinc galvanizing lines,
electrical-grade steel preparation lines (usually present as a
chromate or as chromic acid), and welding/plasma torch
cutting/oxygen lancing on process lines, as well as during
maintenance welding/burning of stainless steel/chromium
alloy steels or welding with certain “sticks,” welding rods
containing chromates on particular carbon-grade steels.
Certain rust inhibitors that are applied to the surface of
carbon-grade steels may also contain hexavalent chromium
in the form of chromates or chromic acid. Furthermore,
certain specialty refractories may contain chromates.
Worker Exposure and Health Consequences
Workplace exposure to Cr (VI) in excess of the OSHA
permissible exposure limit (PEL) may cause the following
health effects:
• Lung cancer in workers who breathe airborne
Cr (VI).
• Irritation or damage to the nose, throat and lungs
(respiratory tract) if Cr (VI) is inhaled.
• Irritation or damage to the eyes and skin if Cr (VI)
contacts these organs.
Workers can inhale airborne Cr (VI) as a dust, fume
or mist while, among other things, producing chromate
pigments, dyes and powders (such as chromic acid and
chromium catalysts); working near chrome electroplating;
performing hot work and welding on stainless steel, highchrome alloys and chrome-coated metal; and applying and
removing chromate-containing paints and other surface
26 ✦ Iron & Steel Technology
coatings. Skin exposure can occur while handling solutions, coatings and cements containing Cr (VI).
OSHA Hexavalent Chromium Standard
On Feb. 28, 2006, the Occupational Safety and Health
Administration (OSHA) published the Hexavalent
Chromium Standard. Three versions of the standard
were issued: General Industry Standard, 1910.1026, the
Construction Industry, 1926.1126 and Maritime, 1515.1026.
The basic requirements are the same in each version.
Cr (VI) exposure from any source is covered under these
standards, except exposure from Portland Cement and the
application of regulated pesticides such as the treatment
of wood with hexavalent chromium–containing pesticides.
However, a hexavalent chromium exposure that may result
from sawing or sanding treated wood is covered by the standard. Each of the standards allows for another exception;
this is where employers have objective data demonstrating
that an arterial-containing chromium or a process involving chromium cannot release Cr+6 in concentrations at or
above 0.5 micrograms per cubic foot of air average for an
eight-hour work shift (0.5 µg/m3, 8-Hr, TWA). The standard that is applicable to the steel industry is the General
Industry Standard, 1910.1026.
As an aside, there is partial exception to certain provisions of the standard if an employer can establish and document that airborne exposures to hexavalent chromium
do not occur for any individual employee or occupation
for 30 days or more in any calendar year. Even under this
scenario, however, should the exposure exceed the PEL for
a particular task, the employee must be provided controls
to reduce exposures to below the PEL on the day the particular work was performed.
The PEL for hexavalent chromium is five micrograms
per cubic foot of air average for an eight-hour work shift
(5.0 µg/m3, 8-Hr, TWA). Occupations found to have airborne hexavalent chromium in excess of the PEL must
be provided controls, engineering, administrative tools,
clothing, hygiene, periodic monitoring and/or respiratory
protection to reduce their actual exposure to below the
PEL. In addition, the standard establishes an Action Level
(AL) or concentration where there are certain requirements, such as medical surveillance, periodic monitoring
and awareness training. Generally speaking, and as is the
case with hexavalent chromium, the OSHA AL is a “trigger
level” that is approximately one-half the PEL. If the AL is
exceeded but remains below the PEL, closer observation
of the occupation and processes is warranted to ensure the
PEL is not exceeded. The AL for Cr+6 is 2.5 µg/m3, 8-Hr,
TWA.
In a very general sense, the OSHA exposure limit for
hexavalent chromium is relatively low, indicative of a
potentially hazardous substance. In order to provide a
Safety First
Figure 1 — Welder being monitored.
Figure 2 — Fume extractor setup through HEPA filter unit.
different perspective, these limits are 10 times lower than
the lead exposure limit (50 µg/m3) and more than 2,000
times lower than the OSHA limit for iron oxide fume (10
mg/m3).
Exposure Assessments
Each employer with a workplace or work operation covered by the standard must initially determine employee
exposures. This initial exposure assessment can be accomplished by means of a “scheduled monitoring option” or a
“performance-oriented option.”
The “scheduled monitoring option” requires air sampling for every occupation with potential hexavalent chromium exposure to make an initial characterization or
assessment of worker exposures. Depending on the exposures found, monitoring might need to be repeated every
3 or 6 months.
Alternatively, the second approach afforded to employers by OSHA is the “performance-oriented option” for
initial determinations or assessments. With this approach,
exposures can be estimated using any combination of
appropriate air sampling historical data or objective data.
Objective data is information, such as air monitoring data
from industry-wide surveys or calculations based on the
composition or chemical and physical properties of a
substance, demonstrating the employee exposure to Cr+6
associated with a particular product or material or a specific process, operation or activity. Air monitoring, in this
case, could incorporate area airborne as well as personal
air sampling. The data must reflect workplace conditions
closely resembling the processes, types of material, control
methods, work practices and environmental conditions in
the employer’s current operations.
Both assessment options, especially the “performanceoriented option,” should be developed in conjunction with
the advice of a board-certified industrial hygienist in comprehensive practice by the American Board of Industrial
Hygiene (ABIH). Sampling plans should be developed and
documented. Results/data need to be maintained, prefer-
ably in both hard copy and electronic. The storage of data
in a computerized data management system will allow for
ease of statistical analyses and retrieval.
The preferred method for sampling and analyzing airborne hexavalent chromium is the OSHA ID-215 Method.
The 37-mm-diameter, 5.0-micron pore size (or 0.8-micron
pore size) polyvinyl chloride (PVC) filter should be utilized
to collect the airborne contaminant. The 37-mm-diameter,
sodium hydroxide pre-treated filter is preferred when
evaluating exposures for chrome plating operations such as
near the tin lines. However, the aforementioned PVC filters
can be used in chrome plating operations, but the lab must
perform post-sampling preparation and must analyze the
filters within six days of the sampling. PVC filters for welding/burning or melting stainless steel/chromium alloys
must be analyzed by the lab within eight days of sampling
due to possible iron II interference. The preference would
be to utilize an American Industrial Hygiene Association
(AIHA) accredited laboratory.
Summary of Hexavalent Chromium Determinations
— Steel Industry
A compilation of the industrial hygiene, airborne hexavalent chromium data from surveys performed by the author
or his team, or industrial hygiene data available to the
author for the steel industry or industries involved with
welding/burning of stainless steel products, is shared
below.
Stainless Steel and High-Chromium-Grade Alloys
More than 1,000 data points, including both personal
and area sampling along with settled dust and surface
wipes, were obtained, representative of six EAF/AOD meltshops/baghouses, four casters, two teeming operations,
five hot rolling mills, eight anneal and pickle lines, four
Midwest grinders, seven slitters, and related process line
welding or torch cutting operations.
Airborne personal and/or area exposures were found to
be generally below the OSHA AL, with a few exceeding the
May 2010 ✦ 27
Safety First
Figure 3 — Fume extractor gun (FEG).
Figure 4 — Welder wearing negative-pressure, air-purifying,
elastomeric respirator equipped with P100 filters.
AL, but in the majority of cases below the PEL. However,
area sample results in the EAF/AOD meltshops, collected
on cranes or crane walkways or elevated locations above the
vessels, were found to range from the AL (2.5 µg/m3) to as
much as 3 or 4 times the PEL.
Bulk, settled dust analysis at three EAF/AOD meltshops
revealed an unexpected result, in that the surface-settled
dust collected at the elevated locations on and near the
meltshop cranes revealed the actual presence of hexavalent
chromium, albeit at concentrations of 0.00005% or less by
weight. It is uncertain if the hexavalent chromium in this
settled dust was residual Cr+6 that had not returned to a
more stable state associated with the melting process, or
chromates from paint on the steel structures that may have
degradated over time.
Figure 5 — Welder’s hood/powered air-purifying respirator
combination with P100 filters.
28 ✦ Iron & Steel Technology
Welding on Stainless Steel and High-Chromium-Grade Alloys
Automatic welders on process lines or hand welding performed in the presence of local exhaust ventilation (LEV)
revealed airborne exposures or concentrations to be less
than both the PEL and the AL.
On the other hand, welding or torch cutting on the process lines or independent maintenance welding tasks on
stainless steel or chromium alloys indicated airborne Cr+6
to vary widely from near the AL to more than 10 times the
PEL.
The extent of employee exposure to hexavalent chromium is dependent on many variables, such as (in the case
of welding/burning) the method of welding and cutting,
the percent of chromium in the base metal or welding rod,
the physical configuration of the work space, the amount
of weld put down, ventilation, positioning of the welder,
etc. These variables must be considered when assessing
exposures.
The most common manual or hand welding is shielded
metal arc welding (SMAW), commonly referred to as
“stick” welding, since welding rods referred to as “sticks”
are used. Hexavalent chromium has been found to make
up 47–62% of the total chromium in the fume generated
by stick welding. Hexavalent chromium is produced when
the welding fluxes in the welding rods combine with oxygen during the welding process to form sodium chromate
and/or potassium chromate. The welding rods are more
responsible for the generation of hexavalent chromium
than the base stainless steel or high-chromium-alloy base
metal. One study revealed that, when the sodium and
potassium content of the coating of E-308 welding rod
was lowered from a 2–5% range to less than 1%, the emission rate for total chromium was reduced by 30% and for
hexavalent chromium by 94%.
In general, the relative amount of hexavalent chromium
in the total welding fume generated for listed types of welding on stainless or high-chromium alloys is presented in
decreasing order:
• Shielded Metal Arc Welding (SMAW) (stick welding).
• Flux Core Arc Welding (FCAW).
• Gas Metal Arc Welding (GMAW) (MIG).
• Gas Tungsten Arc Welding (GTAW) (TIG).
Figure 6 — Portable welding local exhaust ventilation (LEV) unit.
• Submerged Arc Welding (SAW).
Another variable and control is the presence or absence
of local exhaust ventilation or fixed-in-place hood systems
or portable welding fume hoods. Local exhaust ventilation
(LEV) is important during welding or cutting of chromium-containing products with welding rods with sodium- or
potassium-containing fluxes that, in the presence of oxygen
and chromium, form hexavalent chromium–containing
chromates. It is also just as important to place the collection hood from the LEV as close to the generation of the
fume as possible, preferably 6–12 inches from the welding
fume generation point. There are now LEV systems known
as fume extractor guns that capture welding fumes right at
the source of generation through a ventilation intake hood
nozzle located immediately adjacent to the welding gun.
The work practices of individual welders should be
observed in order to assist in minimizing potential airborne hexavalent chromium exposure. Welders should be
encouraged to perform the welding in a position such that
visible fume is moving away and not through the worker’s
breathing zone.
Respiratory protection can be used to reduce the airborne exposure of the worker to concentrations below the
PEL where engineering and work practices alone are inadequate or when exposures to an occupation above the PEL
occur less than 30 times in the year. The exposure results of
air monitoring are used to determine the type of National
Institute of Occupational Safety and Health (NIOSH)
approved respirator that is most appropriate. Table 1 shows
the types of respirators that are appropriate for particular
airborne concentrations.
Carbon Steel Grades and Processes
Exposure and area concentrations for Cr+6 were
obtained at three tin (chrome) lines, 10 galvanizing lines,
eight meltshops/baghouses including low-chromium-alloy
heats (three EAF and five BOF with ladle metallurgical stations), three electrical steel treatment lines. Approximately
500+ data points for hexavalent chromium were collected
and analyzed.
Personal exposures as well as area concentrations have
been below the OSHA AL. The only area monitoring that
revealed the potential to exceed the AL and/or PEL had
been openings to holding tanks with chromic acid/zinc
chromate present, as well as near zinc chromate sprays at
galvanizing lines. It should be kept in mind that personal
exposures for the occupations in these processes or near
these operations have been below the AL. Simple controls,
such as covering open surface tanks, and closing openings
or transfer points for the chromate solutions, were successful in reducing the area concentrations as well.
Summary
• In a very general sense, employee exposure to
hexavalent chromium in the steel industry, including the stainless/specialty steel sector, has been well
below the OSHA PEL and the AL. Certain elevated
areas in stainless steel/high-chromium meltshops
have demonstrated that these areas can at times
have airborne Cr+6 concentrations above the AL
and/or PEL. The existing ventilation controls in the
shops, as well as positive-pressure filtered air units
on cranes and the closure of doors and windows
on the crane operators’ cab, have been effective in
maintaining the exposures to crane operators below
the AL. For those intermittent occasions when maintenance employees have to access and work in these
areas for several hours, the use of respiratory protection has been effective in protecting the employees.
• The tasks or processes with the most potential
concern are those involving welding/torch cutting
and oxygen lancing. Manual welding on stainless
and high-chromium-grade steels using sodium- or
potassium-containing fluxes or coatings resulted
in the potential for the highest exposures of Cr+6
above the PEL. The use of alternative welding
processes or combination of methods — i.e., MIG,
TIG or SAW, lower sodium/potassium-containing
welding rods, use of fume extraction welding guns
and/or local exhaust ventilation, along with work
practices — will result in lower airborne hexavalent
chromium exposure.
• If not already done, conduct initial exposure determinations relative to Cr+6. Review the operations
and processes at the facility, and determine whether
hexavalent chromium may be present. Review the
raw materials, byproducts and products manufactured, chemical inventories, and the material safety
data sheets (MSDSs). Are chromates or chromic
acid solutions used in any of the processes? What
grades and types of steel are being produced? Is
welding/plasma torch cutting performed on stainless steel or high-chromium-grade steel? Create a
spreadsheet to summarize the review.
Type of respirator
Maximum airborne Cr+6
P100 Filtering-face piece, air-purifying
50 µg/m3 (10X PEL)
Elastomeric, half-face, negative pressure, air-purifying
equipped with P100 filters
Elastomeric, full-face, negative-pressure, air-purifying
equipped with P100 filters
Powered air-purifying, full face with welder’s hood
equipped with P100 filters
5000 µg/m3 (1,000X PEL,
with written approval of mfr.)
Supplied-air, positive-pressure, constant flow
5000 µg/m3 (1000X PEL)
50 µg/m3 (10X PEL)
250 µg/m3 (50X PEL)
Table 1 — Respirators for Airborne Concentrations
May 2010 ✦ 29
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Safety First
• Work with an experienced health and safety professional, preferably an industry-experienced, certified industrial hygienist, to determine if baseline,
scheduled monitoring or a performance-oriented
sampling plan for the initial evaluation of hexavalent chromium exposures is most appropriate.
Determine whether existing historic air monitoring
results and the sampling and analytical protocol
that had been utilized were appropriate for Cr (VI).
Evaluate whether the tasks or processes that resulted
in exposures to exceed the PEL occur 30 or more
days a year. Monitor as needed.
• With the results of the initial determinations in
hand, determine the most appropriate controls
that may be required — engineering (i.e., LEV,
isolation, enclosure, substitution, alternate welding processes), administrative (i.e., work practices,
training) and/or respiratory protection. Should
additional monitoring be performed to define the
regulated area(s)? Should task-specific sampling be
incorporated into the sampling strategy to limit the
actual time period or location when respiratory protection is necessary? Work closely with the frontline
employees and operators as well as engineers when
investigating the feasibility of controls.
• Set up a plan to conduct periodic re-evaluations or
assessments, even if initial results had been below
the OSHA AL.
• If required based on the results, establish a medical
surveillance program, training awareness program,
and possible hygiene and personal protective clothing programs. Modify and update the programs
based on the exposure monitoring plan and process/work practice changes.
An understanding of the OSHA standard for hexavalent
chromium is essential in order to develop and implement
practical solutions for the safe handling of hexavalent chromium. Armed with basic information and an understanding of the processes, hexavalent chromium exposures can
be and have been readily controlled, thus protecting our
greatest asset — our employees.
Further reading on the subject of hexavalent chromium
can be obtained from: OSHA’s Web site, www.osha.gov;
the Web site for the state of Washington OSHA, www.lni.
wa.gov/safety; and welding equipment manufacturers’
Web sites.
F
— Bernard J. Quinn, CIH, is president/CEO of AM Health
and Safety Inc. He is also vice chair of AIST’s Safety & Health
Technology Committee.
If you have questions about this topic or other safety issues,
please contact [email protected]. Please include your
full name, company name, mailing address and e-mail
in all correspondence.