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Objective:
Health data and legal suits are causing Occupational Safety
and Health Administration (OSHA) regulators to consider lowering
the hexavalent chromium exposure limit. It is anticipated
that future exposure limits could be established at levels
between 20- and 200-fold below the current level of 52 micrograms
per cubic meter (µg/m3) as chromium. At present, hexavalent
chromium emissions from hard chromium electroplating baths
are controlled by ventilation of the workplace, extraction
fans, and use of an air pollution control device (APCD), which
is typically a mist eliminator/wet scrubber, to remove chromium
from the exhaust air stream. The Environmental Protection
Agency (EPA) regulates emissions of hexavalent chromium to
the outside atmosphere. This project investigated a 0.25 percent
addition of a perfluorinated compound named Fumetrol®
140, a third generation wetting agent/fume suppressant (WA/FS),
to hard chromium electroplating baths at the Naval Aviation
Depot in Cherry Point, North Carolina and at the Oklahoma
City Air Logistics Center at Tinker Air Force Base, Oklahoma.
Technology
Description:
Hexavalent
chromium electroplating baths generate gases (i.e., hydrogen
and oxygen) at the electrodes, which rise and create a mist
of chromic acid as they burst at the surface. A WA/FS decreases
the surface tension of a plating bath, which reduces the size
of the bubbles and diminishes their impact as they escape
at the surface. As a consequence, emissions of hexavalent
chromium and worker exposure are greatly reduced. Fumetrol®
140 is relatively soluble in water and produces very little
foam, making it easy to use.
Results:
Worker
exposure to hexavalent chromium emissions was reduced. Air
quality was approximately two to four times better with Fumetrol®
140 addition. However, even without Fumetrol® 140 addition,
the most stringent proposed OSHA standard of 0.5 µg/m3
chromium was never exceeded. There was a 20- to 70-fold reduction
in total chromium emissions in the exhaust air stream when
the Fumetrol® 140 was used. In most cases, the exhaust
chromium concentration was below the 30 µg/m3 chromium
standard for small, existing tanks but did not attain the
15 µg/m3 chromium standard for new tanks. No adverse
effects on the quality of the electroplated chromium or the
steel alloys on which it was deposited were detected.
Benefits
and Implications:
An
average savings of $2,000 per year per tank was estimated
for chromic acid that does not escape. Ventilation rates and
associated energy costs would be reduced, and fewer or smaller
APCDs might be necessary for a new electroplating plant. Wastewater
treatment costs would also be reduced if an APCD were no longer
required. For an existing system, the payback period on the
minimal modifications necessary would range from under 7 months
(if the APCD were turned off) to less than three years (if
the APCD remained in use). In the future, it is possible that
the EPA may consider allowing the control of hard chromium
electroplating tank emissions through the use of a WA/FS alone,
which would only require surface tension measurements for
monitoring. (Project Completed - 2003)
References:
- ESTCP
Cost and Performance Report. November 2003. (PDF File
Format)
Contact:
Ms.
Kathleen Paulson
Naval Facilities Engineering Service Center
1100 23rd Avenue, Code 425
Port Hueneme, CA 93043-4370
Telephone: (805) 982-4984
Fax: (805) 982-1409
E-mail: kathleen.paulson@navy.mil
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