Health and Safety / Fire Protection
Hexavalent Chromium Risk
Does your facility have hexavalent chromium dust, mist, or fumes in the air? Don't say no too quickly! The Occupational Safety and Health Administration (OSHA) has issued more stringent safety and health rules for businesses to comply with hexavalent chromium, or Cr(VI), requirements. The new standards reduce the permissible exposure limits by more than 90 percent. To protect your workers, reduce your liability and remain in compliance, you need to be familiar with these new OSHA standards and the causes and effects of chromium dust.
Many production processes at industrial companies, construction companies and shipyards result in chromium dust particles being released into the air. Hexavalent chromium compounds are widely used in the chemical industry as ingredients and catalysts in pigments for dyes, paints, inks, and plastics; in chromates added as anti-corrosive agents to paints, primers, and other surface coatings; and in chromic acid electroplating. Cr(VI) can also be produced when welding on stainless steel or chromium painted surfaces.
You may not even be aware of this health hazard in your facility because you may not be directly using chromium hexavalent compounds in your production. But if you do contract work on materials, parts and components provided to you by other companies then you might be producing chromium hexavalent dust particles, thus falling under the new and more rigorous OSHA guidelines.
Hexavalent chromium dust, mist or fumes can contaminate hands, clothing, beards, food and beverages, and the long-term health effects can be serious. The primary means of human exposure to hexavalent chromium and chromate salts are inhalation, ingestion and skin contact. Hexavalent chromium is considered a potential lung carcinogen and long-term health effects can include lung cancer, asthma, nasal ulceration and even perforation of the septum (the wall separating the nasal passages), as well as skin dermatitis and ulcerations. Affected organs can include the respiratory system, liver, kidneys, eyes and skin. For your company, this is a hazard and a potential liability that needs to be addressed.
The preferred approach to managing this air quality hazard is to use engineering controls such as proper ventilation or equipment and process modification. Air Purification, Inc. can help your company meet and exceed the new OSHA rules. Please contact us today to discuss this issue and to learn methods of indoor air quality improvement, total facility ambient air filtration, source capture methods, and blow off decontamination to remove airborne contaminants at the source.
Chromium hexavalent (CrVI) compounds, often called hexavalent chromium, exist in several forms. Industrial uses of hexavalent chromium compounds include chromate pigments in dyes, paints, inks, and plastics; chromates added as anticorrosive agents to paints, primers, and other surface coatings; and chromic acid electroplated onto metal parts to provide a decorative or protective coating. Hexavalent chromium can also be formed when performing "hot work" such as welding on stainless steel or melting chromium metal. In these situations the chromium is not originally hexavalent, but the high temperatures involved in the process result in oxidation that converts the chromium to a hexavalent state.
Exposures to hexavalent chromium (Cr(VI)) are addressed in specific standards for the general industry, rules concerning OSHA access to employee medical reports, shipyard employment, marine terminals, and the construction industry.
This section highlights OSHA standards, Federal Registers (rules, proposed rules, and notices), directives (instructions for compliance officers), and standard interpretations (official letters of interpretation of the standards) related to Cr(VI).
Note: Twenty-five states, Puerto Rico and the Virgin Islands have OSHA-approved State Plans and have adopted their own standards and enforcement policies. For the most part, these States adopt standards that are identical to Federal OSHA. However, some States have adopted different standards applicable to this topic or may have different enforcement policies.
OSHA on Welding & Dust Control
Ventilation for general welding and cutting.
General. Mechanical ventilation shall be provided when welding or cutting is done on metals not covered in paragraphs (c)(5) through(c)(12) of this section. (For specific materials, see the ventilation requirements of paragraphs (c)(5) through (c)(12) of this section.)
In a space of less than 10,000 cubic feet (284 m(3)) per welder.
In a room having a ceiling height of less than 16 feet (5 m).
In confined spaces or where the welding space contains partitions, balconies, or other structural barriers to the extent that they significantly obstruct cross ventilation.
Minimum rate. Such ventilation shall be at the minimum rate of 2,000 cubic feet (57 m(3)) per minute per welder, except where local exhaust hoods and booths as per paragraph (c)(3) of this section, or airline respirators approved by the U.S. Bureau of Mines for such purposes are provided. Natural ventilation is considered sufficient for welding or cutting operations where the restrictions in paragraph (c)(2)(i) of this section are not present.
Local exhaust hoods and booths. Mechanical local exhaust ventilation may be by means of either of the following:
Hoods. Freely movable hoods intended to be placed by the welder as near as practicable to the work being welded and provided with a rate of air-flow sufficient to maintain a velocity in the direction of the hood of 100 linear feet (30 m) per minute in the zone of welding when the hood is at its most remote distance from the point of welding. The rates of ventilation required to accomplish this control velocity using a 3-inch (7.6 cm) wide flanged suction opening are shown in the following table:
|Welding Zone||Minimum |
air flow (1)
cubic feet / minutes
|4 to 6 inches from arc or torch||150||3|
|6 to 8 inches from arc or torch||275||3 1/2|
|8 to 10 inches from arc or torch||425||4 1/2|
|10 to 12 inches from arc or torch||600||5 1/2|
Footnote(1) When brazing with cadmium bearing materials or when cutting on such materials increased rates of ventilation may be required.
Footnote(2) Nearest half-inch duct diameter based on 4,000 feet per minute velocity in pipe.
Fixed enclosure. A fixed enclosure with a top and not less than two sides which surround the welding or cutting operations and with a rate of airflow sufficient to maintain a velocity away from the welder of not less than 100 linear feet (30 m) per minute.
Ventilation in confined spaces.
Air replacement. All welding and cutting operations carried on in confined spaces shall be adequately ventilated to prevent the accumulation of toxic materials or possible oxygen deficiency. This applies not only to the welder but also to helpers and other personnel in the immediate vicinity. All air replacing that withdrawn shall be clean and respirable.
Airline respirators. In circumstances for which it is impossible to provide such ventilation, airline respirators or hose masks approved for this purpose by the National Institute for Occupational Safety and Health (NIOSH) under 42 CFR part 84 must be used.
Self-contained units. In areas immediately hazardous to life, a full-facepiece, pressure-demand, self-contained breathing apparatus or a combination full-facepiece, pressure-demand supplied-air respirator with an auxiliary, self-contained air supply approved by NIOSH under 42 CFR part 84 must be used.
Outside helper. Where welding operations are carried on in confined spaces and where welders and helpers are provided with hose masks, hose masks with blowers or self-contained breathing equipment approved by the Mine Safety and Health Administration and the National Institute for Occupational Safety and Health, a worker shall be stationed on the outside of such confined spaces to insure the safety of those working within.
Oxygen for ventilation. Oxygen shall never be used for ventilation.
General. In confined spaces, welding or cutting involving fluxes, coverings, or other materials which contain fluorine compounds shall be done in accordance with paragraph (c)(4) of this section. A fluorine compound is one that contains fluorine, as an element in chemical combination, not as a free gas.
Maximum allowable concentration. The need for local exhaust ventilation or airline respirators for welding or cutting in other than confined spaces will depend upon the individual circumstances. However, experience has shown such protection to be desirable for fixed-location production welding and for all production welding on stainless steels. Where air samples taken at the welding location indicate that the fluorides liberated are below the maximum allowable concentration, such protection is not necessary.
Confined spaces. In confined spaces welding or cutting involving zinc-bearing base or filler metals or metals coated with zinc-bearing materials shall be done in accordance with paragraph (c)(4) of this section.
Indoors. Indoors, welding or cutting involving zinc-bearing base or filler metals coated with zinc-bearing materials shall be done in accordance with paragraph (c)(3) of this section.
Confined spaces. In confined spaces, welding involving lead-base metals (erroneously called lead-burning) shall be done in accordance with paragraph (c)(4) of this section.
Indoors. Indoors, welding involving lead-base metals shall be done in accordance with paragraph (c)(3) of this section.
Local ventilation. In confined spaces or indoors, welding or cutting operations involving metals containing lead, other than as an impurity, or metals coated with lead-bearing materials, including paint, must be done using local exhaust ventilation or airline respirators. Such operations, when done outdoors, must be done using respirators approved for this purpose by NIOSH under 42 CFR part 84. In all cases, workers in the immediate vicinity of the cutting operation must be protected by local exhaust ventilation or airline respirators.
Beryllium. Welding or cutting indoors, outdoors, or in confined spaces involving beryllium-containing base or filler metals shall be done using local exhaust ventilation and airline respirators unless atmospheric tests under the most adverse conditions have established that the workers' exposure is within the acceptable concentrations defined by 1910.1000 of this part. In all cases, workers in the immediate vicinity of the welding or cutting operations shall be protected as necessary by local exhaust ventilation or airline respirators.
General. In confined spaces or indoors, welding or cutting operations involving cadmium-bearing or cadmium-coated base metals must be done using local exhaust ventilation or airline respirators unless atmospheric tests under the most adverse conditions show that employee exposure is within the acceptable concentrations specified by 29 CFR 1910.1000. Such operations, when done outdoors, must be done using respirators, such as fume respirators, approved for this purpose by NIOSH under 42 CFR part 84.
Confined space. Welding (brazing) involving cadmium-bearing filler metals shall be done using ventilation as prescribed in paragraph (c)(3) or (c)(4) of this section if the work is to be done in a confined space.
Mercury. In confined spaces or indoors, welding or cutting operations involving metals coated with mercury-bearing materials, including paint, must be done using local exhaust ventilation or airline respirators unless atmospheric tests under the most adverse conditions show that employee exposure is within the acceptable concentrations specified by 29 CFR 1910.1000. Such operations, when done outdoors, must be done using respirators approved for this purpose by NIOSH under 42 CFR part 84.
Manufacturer's instructions. In the use of cleaning materials, because of their possible toxicity or flammability, appropriate precautions such as manufacturers instructions shall be followed.
Degreasing. Degreasing and other cleaning operations involving chlorinated hydrocarbons shall be so located that no vapors from these operations will reach or be drawn into the atmosphere surrounding any welding operation. In addition, trichloroethylene and perchlorethylene should be kept out of atmospheres penetrated by the ultraviolet radiation of gas-shielded welding operations.
Cutting of stainless steels. Oxygen cutting, using either a chemical flux or iron powder or gas-shielded arc cutting of stainless steel, shall be done using mechanical ventilation adequate to remove the fumes generated.
National Fire Prevention Association
FAQs: A Practical Discussion of NFPA 484 and the Use of Wet Dust Collectors*
- Does the code apply to me?
- Who enforces the code?
- What does this code say in plain language?
- What are the basic dangers?
- What is the most common practice in handling combustible dust?
- How do I test my dust?
If you process or finish metals that can create explosive dusts, (Aluminum, Magnesium, Niobium, Tantalum, Titanium, or Zirconium), one way or another NFPA 484 Standard for Combustible Metals applies to you. If you are in a US city, then this code is part of the fire code and is a part of the building code. If your city has adopted the International Building code, it also refers back to the NFPA code. OSHA and your own fire and liability insurance carrier may also have an interest in your compliance to this code.
The most common enforcement comes through the Fire Marshal. This is simply because on the local level, the Fire Marshal is charged with the job of understanding the code and how to apply it. However, the authority having jurisdiction (AHJ) can be anyone who is a public safety officer or inspector. Fire, health, or labor workers are all able to enforce the code if you are in their city or jurisdiction. The AHJ may also interpret the code when that is necessary. OSHA is getting more involved with the issue of compliance to the code as the concerns for worker safety increase.
NFPA 484 is the standard for all combustible metals. Most of the code applies to a small part of the industry that actually manufactures metal powders. However, 484 Chapter 6 addresses Aluminum, and Section 6.3 is dedicated to processing and finishing operations.
Here are some of the "Dos and Don'ts" relating to dust collection systems and collector design.
- Do connect all dust producing equipment to hoods that capture and transport the dust.
- Do not mix the buffing-polishing with the grinding.
- Do keep your duct velocity at 4500 feet per minute.
- Do not allow the minimum explosible concentration (MEC) of the dust to occur. (This is a problem with vacuum cleaners.)
- Do use metal, not plastic, duct and keep the duct system simple and smooth, with seams downstream and as straight as you can.
- Do not install any dead spots or ports for future use.
- Do bond and electrically ground all the machines, the duct, and the dust collector itself.
- Do not mix any other metals with Aluminum in a dry collector or in any ducting.
Wet Dust Collectors -- Minimum Design Features:
- The blower must be on the clean side.
- The collector cannot have any un-vented pockets (hydrogen
- The efficiency must be high if you plan to recirculate the air.
- The wet unit should be as close to the dust generation as possible.
- No after-filters are allowed (for Aluminum).
- Mix the sludge with dry clay (kitty litter) to make sure it is safe, i.e., to prevent it from overheating and giving off hydrogen.
Dry Dust Collectors -- Special Instructions:
- The collector must be located outside the building.
- The collector must have explosive venting, barriers and warning signs regarding using the collector for Aluminum only and a warning about the contents being explosive dust.
- Portable collectors must be limited to one pound of dust.
- Do not mix any other metals with Aluminum in a dry collector or in any ducting.
- The filter media must be grounded.
- The blower must be on the clean side.
- No electrostatic collectors are permitted.
- Water condensation must be prevented.
- There must be no accumulation of dust anywhere in the collector except for inside the dust receptacle.
(For added comments on safety considerations for Dry Dust Collectors, see the Annex A.220.127.116.11.2 below.)
The dangers involve the risk of fires and explosions. Here are a few real world examples:
- A dry downdraft table used for Aluminum finishing is set on fire when a employee sharpens a knife on lunch break.
- A young man is burned badly when he uses a bench grinder normally used for Steel to grind away aluminum rivets.
- While sanding Aluminum parts, a worker is badly injured when a small collector with a Steel blower wheel on the dirty side of the filter explodes.
Other examples of potential dangers include:
- Aluminum and Steel together burn very very hot and are used in the military to melt away Steel parts in the field. Mixing the two metals can be very dangerous.
- Steel parts or Steel grating in the workplace where Aluminum or Magnesium grinding occurs provide a high risk of sparks.
- Common shop vacuum cleaners can be very dangerous due to the likelihood of creating an explosive fuel/air mixture in the vacuum hose and in the canister. If a static charge spark occurs, the risk of explosion is high.
Wet unit sales indicate a move in the industry to the wet dust collector for finishing applications for almost all Aluminum, Magnesium or Titanium alloys. Recent improvements in the design of the wet unit provide even better reliability and a lower cost of operation. Wet dust collectors offer the kind of peace of mind that busy plant, safety and maintenance managers desire.
Testing is not necessary in most cases. The dust deflagration index, or the K value, is known to be in the highest category for these metals. Metal dusts that are produced in a grinding and finishing operations tend to vary widely in particle size and in chemistry (the alloy and degree of oxidation) that affect volatility. Most all of the operations are below the size that is considered flammable (420 microns) and the size that wet collectors are able to filter at high efficiency (5 microns). Most all mechanical (not thermal) dust-generating operations produce particles above 10 microns. If a wet collector is used, it is the best available technology for safety with all of the dust variables.
Excerpt: Additional discussion on the use of Dry Dust Collectors for combustible dusts:
A.18.104.22.168.2 A high-efficiency cyclone-type collector presents less hazard than a bag- or media-type collector and, except for extremely fine powders, will usually operate with fairly high collection efficiency. Where cyclones are used, the exhaust fan discharges to atmosphere away from other operations. It should be recognized that there will be some instances in which a centrifugal-type collector can be followed by a fabric- or bag-type, or media-type collector or by a scrubber-type collector where particulate emissions are kept at a low level. The hazards of each collector should be recognized and protected against. In each instance, the fan will be the last element downstream in the system. Because of the extreme hazard involved with a bag- or mediatype collector, consideration should be given to a multiple-series cyclone with a liquid final stage.
Industry experience has clearly demonstrated that an eventual explosion can be expected where a bag- or media-type collector is used to collect aluminum fines. Seldom, if ever, can the source of ignition be positively identified. In those unusual instances when it becomes necessary to collect very small fines for a specific commercial product, it is customary for the producer to employ a bag- or mediatype collector. With the knowledge that strong explosive potential is present, the producer will locate the bag- or media-type collector a safe distance from buildings and personnel.
If a bag- or media-type collector is used, the shaking system or dust removal system can be such as to minimize sparking due to frictional contact or impact. Pneumatic- or pulse-type cleaning is more desirable because no mechanical moving parts are involved in the dusty atmosphere. If the bags are provided with grounding wires, they can be positively grounded through a low-resistance path to ground. Where bags are used, it is customary that the baghouse be protected by an alarm to indicate excessive pressure drop across the bags. An excess air temperature alarm is also frequently employed. A bag- or media-type collector is customarily located at least 15 m (50 ft) from any other building or operation. It is not customary to permit personnel to be within 15 m (50 ft) of the collector during operation or when shaking bags. Explosion vents are usually built into the system, as described in NFPA 68, Guide for Venting of Deflagrations. Care is customarily exercised in locating the vents because of the possibility of blast damage to personnel or adjacent structures.
*Note: This is an informal industry discussion of NFPA 484 for the purpose of providing a practical understanding of its requirements and the helpfulness of wet dust collectors in meeting safety concerns. To confirm code requirements and enforcement for your facility, please refer questions to your local Fire Marshal and/or contact OSHA or the NFPA. A copy of NFPA 484 may be purchased through the NFPA or viewed as a read-only online version by submitting your profile information at: nfpa.org
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