U.S. Department of Labor Occupational Safety and Health Administration Directorate of Technical Support & Emergency Management Office of Science and Technology Assessment

Carbon Monoxide Explosion Hazards in Electric Arc Furnace Steelmaking Operations

Safety and Health Information Bulletin SHIB 12-04-15

Although water explosion hazards in This Safety and Health Information Bulletin is not a standard or regulation, and it creates no new legal electric arc furnaces (EAFs) are well obligations. The Bulletin is advisory in nature, known in the steelmaking industry, informational in content, and is intended to assist explosions caused by excess carbon employers in providing a safe and healthful workplace. Pursuant to the Occupational Safety and monoxide concentrations in the furnace Health Act, employers must comply with hazard- headspace during the reduction of specific safety and health standards and regulations carbon content (decarburization) are an promulgated by OSHA or by a state with an OSHA-approved state plan. In addition, pursuant to emerging concern. As the steelmaking Section 5(a)(1), the General Duty Clause of the industry expands EAF use to melt and Act, employers must provide their employees with a workplace free from recognized hazards likely to refine scrap metal during recycling cause death or serious physical harm. Employers operations, the potential for explosions can be cited for violating the General Duty Clause increases. Explosions can result in if there is a recognized hazard and they do not take reasonable steps to prevent or abate the hazard. serious injury or death to workers. A However, failure to implement any recent near-fatal carbon monoxide recommendations in this Safety and Health explosion during EAF operations Information Bulletin is not, in itself, a violation of the General Duty Clause. Citations can only be highlights the need to ensure that based on standards, regulations, and the General Duty Clause. employers are aware of the hazards and that they establish safe work practices to prevent explosions. EAF operators use the decarburization process, involving oxygen injection from burners under the furnace, to achieve Introduction specific carbon levels in the hot steel bath. EAFs use high-powered electric arcs for EAFs are often used in steelmaking melting scrap along with oxygen reactions in operations to produce carbon steels, as well “the heat” for melting/refining scrap into as stainless and alloy steels, primarily by steel. EAFs typically melt and refine scrap at recycling scrap. EAF operators must around 2,900°F, with capacities over 100 carefully plan and control the tons. melting/refining process to achieve specified carbon content targets needed for the final Operating EAFs present explosion hazards steel products. that may result in death or significant injury to workers. If a large explosion occurs inside an EAF, the furnace contents and flames are ejected at a high blast overpressure and entering through furnace openings. The temperature. When furnace process controls EAF’s ventilation system is designed to are inadequate, explosions can occur if remove the carbon dioxide from the flammable gas mixtures form over “the headspace. heat.” However, if oxygen is rapidly injected into Terminology the hot steel bath, decarburization can proceed so rapidly that carbon monoxide Blast overpressure refers to a sudden pressure overwhelms the ventilation system and may wave after an explosion. accumulate in the headspace. The increased Charge refers to scrap metal prepared for melting carbon monoxide generation consumes all in an EAF. Once the melting process begins, the available oxygen, which is necessary to charge is referred to as “the heat.” convert carbon monoxide to carbon dioxide. The unreacted carbon monoxide can become Decarburization is the process used to reduce the carbon content in steelmaking. highly concentrated in the EAF headspace. If the carbon monoxide concentration in the Hot steel bath is the molten steel generated in the headspace reaches the explosive range, EAF. between 12.5 to 74.2 percent, any sudden Headspace refers to the unoccupied space in the addition of oxygen-containing air into the EAF containing gaseous byproducts vaporized enclosed furnace can react with the excess from the hot steel bath. These gases are either carbon monoxide and form an explosive reacted during the steelmaking process or drawn mixture. The high temperature from “the off into the ventilation system as waste. heat” helps cause such a sudden oxidation Off-gas refers to gases present in the headspace. reaction and provides a ready ignition Off-gases vaporize from the hot steel bath. source.

Slag is a steelmaking byproduct formed after How Can Failing to Investigate Smaller separating the metal. Explosions Contribute to a Severe Incident?

How Can the Decarburization Process Implementing safe work practices is critical Cause an Explosion? for preventing EAF explosions. At the steel plant in the case study described below, the The employer generally accepted small carbon decarburization Because carbon monoxide monoxide explosions as normal and process begins is a flammable gas, the operators considered them a routine when the EAF carbon monoxide occurrence during EAF operations. Upon concentration in the EAF operators inject headspace needs careful investigation, OSHA found that the plant oxygen via burners monitoring and control to never addressed these frequent smaller in the furnace to prevent it from reaching explosions and no carbon monoxide convert excess the explosive range. monitoring or furnace process control efforts carbon in “the were used to investigate or prevent them. heat” to carbon Instead, the employer allowed workers to monoxide. The carbon monoxide is unsafely use furnace rocking, or tilting, to converted to carbon dioxide by the oxygen aim flames and furnace contents ejected in the headspace as well as by oxygen from small explosions into the pouring side.

Employers Case Study: Near-Fatal Incident should In May 2013, a sudden reaction and explosion consider occurred in a 165-ton capacity EAF that exposed small carbon three workers on the furnace floor to liquid steel, slag, monoxide and flames of over 3,000°F that ejected from furnace openings. As shown in Fig.1, the explosion was so explosions as powerful that it broke through the outer explosion- proof glass and protective inner windows surrounding “near miss” incidents. To the pulpit (i.e., control booth). Even though all workers wore required PPE, the explosion severely prevent a Figure 1: Pulpit Windows Damaged by burned the three workers on the furnace floor who serious Explosion were hospitalized and treated at the regional burn incident and center. worker injury or death, employers should Likely Causes of Incident conduct a follow up investigation to identify The employer did not provide adequate furnace root causes for flames escaping from furnace process controls and allowed unsafe informal practices to take the place of written procedures openings as well as for small carbon established through a workplace hazard assessment. monoxide explosions. The near-fatal explosion occurred when EAF operators tilted the furnace and oxygen-containing air suddenly entered the headspace. This formed an How to Prevent Carbon Monoxide explosive mixture with excess carbon monoxide that Explosions in EAFs accumulated in the decarburization process. Prior to this incident, sample readings found an OSHA recommends the following to reduce unusually high carbon content in the hot steel bath. or eliminate explosions from excess carbon As a result, EAF operators began performing an monoxide concentrations during extended decarburization process to reduce the carbon content to the pre-specified target. The following decarburization in EAFs: chain of events describes unsafe practices that led to • Train workers on how to recognize and the explosion: avoid unsafe EAF operations associated • Initially, some EAF burners were run on high to inject more oxygen than usual into the bath at a with excess carbon monoxide high injection rate, according to this plant’s concentrations during decarburization. informal routine practice. • Verify that the off-gas analyzer system • Reactions from this rapid oxygen injection generated carbon monoxide at a rate that accurately measures off-gas overwhelmed the EAF ventilation system and accumulation in the furnace. consumed all oxygen in the headspace, creating • excess carbon monoxide over “the heat” in the Use off-gas composition analyses to EAF (instead of the normal furnace process of control the oxygen injection rate and conversion to carbon dioxide). ensure that gas mixtures above “the • Positive pressure in the EAF from the increased carbon monoxide concentration also prevented the heat” stay well below the lower limit of air influx from furnace openings that was the carbon monoxide explosive range, necessary to replenish the oxygen. between 12.5 to 74.2 percent. • Flames from inside the EAF headspace escaped from furnace openings, indicating that small • Ensure that proper furnace ventilation carbon monoxide explosions were occurring inside along with off-gas composition analyses the EAF, but no written procedures existed at this are used to help control chemical plant to monitor or control excess carbon monoxide concentrations in the EAF headspace. reactions in the EAF headspace. • After tilting the EAF, as informal routine practice • Do not consider smaller explosions as after small explosions, carbon monoxide escaped acceptable and immediately investigate through the slag door and other furnace openings, suddenly pulling oxygen-containing air from the their cause to modify furnace process pouring side into the headspace and causing a controls to prevent them. violent explosion.

How OSHA Can Help • Control furnace tilting during EAF OSHA's On-site Consultation Program offers free and operations to help avoid creating confidential advice to small and medium-sized businesses in potentially explosive gas mixtures. all states across the country, with priority given to high- hazard worksites. On-site Consultation services are independent of OSHA enforcement and do not result in How to Protect Workers from Carbon penalties or citations. Consultants from state agencies or Monoxide Explosion Hazards in EAFs universities work with employers to identify workplace hazards, provide advice on compliance with OSHA standards, and assist in establishing safety and health OSHA recommends the following to protect management systems. To locate the OSHA On-site workers from explosion hazards in EAFs: Consultation office in your state, call 1-800-321-OSHA (6742) or visit OSHA's Consult at ion web page. • Ensure that engineering controls (e.g., O SHA Approved State Plans: T wen ty -seven states and 3 shields or shelters) adequately protect U.S. territories operate their own occupational safety and workers from maximum potential blast health state plan approved by OSHA. A list of state plans is overpressure, heat gradients, and struck- available at: www.osha.gov/dcsp/osp/index.html. by hazards from explosions. OSHA Compliance Assistance: OSHA’s compliance • Develop and implement written assistance specialists throughout the nation provide information to employers and workers about OSHA procedures for workers to stand behind st andards, right s and responsibilit ies under t he Occupational shields or shelters when on the furnace Safety and Health Act, present short educational programs floor or to remain in the control booth, to on special hazards and help with other compliance assistance resources. Contact your local OSHA office for the maximum extent possible. more information by calling 1-800-321-OSHA (6742) or • Develop and implement written visit OSHA's web page at www.o sh a.go v . procedures to detect and control excess Workers' Rights carbon monoxide concentrations in the Workers have the right to: EAF headspace. . Working conditions that do not pose a risk of • Ensure that procedures for alarms or serious harm. signals to workers on the furnace floor . Receive information and training (in a language alert them when potentially hazardous and vocabulary they can understand) about conditions occur (e.g., if off-gas analyses workplace hazards, methods to prevent harm, and indicate carbon monoxide buildup). the OSHA standards that apply to their workplace. . Review records of work-related injuries and OSHA also requires employers to ensure illnesses. that workers use PPE that will adequately . Get copies of test results that find and measure protect against explosion hazards in EAFs hazards. (see 29 CFR 1910.132(a) and . File a complaint asking OSHA to inspect their workplace if they believe there is a serious hazard 1910.132(d)(1)(i)). or that their employer is not following OSHA's rules. OSHA will keep all identities confidential. For more relevant resources visit OSHA’s . Exercise their rights under the law without Scrap Metal Recycling Webpage and retaliation or discrimination. OSHA’s Basic Steel Products Webpage. For more information, see OSHA's web page for workers. Contact OSHA For questions or to get information or advice, to report an emergency, report a fatality or catastrophe, file a confidential complaint, order publications, or to request OSHA's free On-site Consultation service, contact your nearest OSHA office, visit www.o sh a.go v , or call OSHA at 1-800-321-OSHA (6742), TTY 1-877-889-5627.