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

Introduction

EAFs are often used in steelmaking 

operations to produce carbon steels, as well 

as stainless and alloy steels, primarily by 

recycling scrap. EAF operators must 

carefully plan and control the 

melting/refining process to achieve specified 

carbon content targets needed for the final 

steel products.

EAF operators use the decarburization 

process, involving oxygen injection from 

burners under the furnace, to achieve 

specific carbon levels in the hot steel bath. 

EAFs use high-powered electric arcs for 

melting scrap along with oxygen reactions in 

“the heat” for melting/refining scrap into 

steel. EAFs typically melt and refine scrap at 

around 2,900°F, with capacities over 100 

tons. 

Operating EAFs present explosion hazards 

that may result in death or significant injury 

to workers. If a large explosion occurs inside 

an EAF, the furnace contents and flames are 

This Safety and Health Information Bulletin is not

a standard or regulation, and it creates no new legal 

obligations. The Bulletin is advisory in nature, 

informational in content, and is intended to assist 

employers in providing a safe and healthful 

workplace. Pursuant to the Occupational Safety and 

Health Act, employers must comply with hazardspecific safety and health standards and regulations 

promulgated by OSHA or by a state with an 

OSHA-approved state plan. In addition, pursuant to 

Section 5(a)(1), the General Duty Clause of the 

Act, employers must provide their employees with 

a workplace free from recognized hazards likely to 

cause death or serious physical harm. Employers 

can be cited for violating the General Duty Clause 

if there is a recognized hazard and they do not take 

reasonable steps to prevent or abate the hazard. 

However, failure to implement any 

recommendations in this Safety and Health 

Information Bulletin is not, in itself, a violation of 

the General Duty Clause. Citations can only be 

based on standards, regulations, and the General 

Duty Clause.

Although water explosion hazards in 

electric arc furnaces (EAFs) are well 

known in the steelmaking industry, 

explosions caused by excess carbon 

monoxide concentrations in the furnace 

headspace during the reduction of 

carbon content (decarburization) are an 

emerging concern. As the steelmaking 

industry expands EAF use to melt and 

refine scrap metal during recycling 

operations, the potential for explosions 

increases. Explosions can result in 

serious injury or death to workers. A 

recent near-fatal carbon monoxide 

explosion during EAF operations 

highlights the need to ensure that 

employers are aware of the hazards and 

that they establish safe work practices to 

prevent explosions.

SHIB 12-04-15
Terminology

Blast overpressure refers to a sudden pressure 

wave after an explosion.

Charge refers to scrap metal prepared for melting 

in an EAF. Once the melting process begins, the 

charge is referred to as “the heat.”

Decarburizationis the process used to reduce the 

carbon content in steelmaking.

Hot steel bath is the molten steel generated in the 

EAF.

Headspace refers to the unoccupied space in the 

EAF containing gaseous byproducts vaporized 

from the hot steel bath. These gases are either 

reacted during the steelmaking process or drawn 

off into the ventilation system as waste. 

Off-gas refers to gases present in the headspace. 

Off-gases vaporize from the hot steel bath. 

Slag is a steelmaking byproduct formed after 

separating the metal.

ejected at a high blast overpressure and 

temperature. When furnace process controls 

are inadequate, explosions can occur if 

flammable gas mixtures form over “the 

heat.”

How Can the Decarburization Process 

Cause an Explosion? 

The 

decarburization 

process begins 

when the EAF 

operators inject 

oxygen via burners 

in the furnace to 

convert excess 

carbon in “the 

heat” to carbon 

monoxide. The carbon monoxide is 

converted to carbon dioxide by the oxygen 

in the headspace as well as by oxygen 

entering through furnace openings. The

EAF’s ventilation system is designed to 

remove the carbon dioxide from the 

headspace.

However, if oxygen is rapidly injected into 

the hot steel bath, decarburization can 

proceed so rapidly that carbon monoxide 

overwhelms the ventilation system and may 

accumulate in the headspace. The increased 

carbon monoxide generation consumes all 

available oxygen, which is necessary to 

convert carbon monoxide to carbon dioxide. 

The unreacted carbon monoxide can become 

highly concentrated in the EAF headspace. 

If the carbon monoxide concentration in the 

headspace reaches the explosive range, 

between 12.5 to 74.2 percent, any sudden 

addition of oxygen-containing air into the 

enclosed furnace can react with the excess 

carbon monoxide and form an explosive 

mixture. The high temperature from “the 

heat” helps cause such a sudden oxidation 

reaction and provides a ready ignition 

source.

How Can Failing to Investigate Smaller 

Explosions Contribute to a Severe 

Incident?

Implementing safe work practices is critical 

for preventing EAF explosions. At the steel 

plant in the case study described below, the 

employer generally accepted small carbon 

monoxide explosions as normal and 

operators considered them a routine 

occurrence during EAF operations. Upon 

investigation, OSHA found that the plant 

never addressed these frequent smaller 

explosions and no carbon monoxide 

monitoring or furnace process control efforts 

were used to investigate or prevent them. 

Instead, the employer allowed workers to 

unsafely use furnace rocking, or tilting, to 

aim flames and furnace contents ejected 

from small explosions into the pouring side.

Because carbon monoxide 

is a flammable gas, the 

carbon monoxide 

concentration in the EAF 

headspace needs careful 

monitoring and control to 

prevent it from reaching 

the explosive range.
Employers 

should 

consider 

small carbon 

monoxide 

explosions as 

“near miss” 

incidents. To 

prevent a 

serious 

incident and 

worker injury or death, employers should 

conduct a follow up investigation to identify 

root causes for flames escaping from furnace 

openings as well as for small carbon 

monoxide explosions.

How to Prevent Carbon Monoxide 

Explosions in EAFs

OSHA recommends the following to reduce

or eliminate explosions from excess carbon 

monoxide concentrations during 

decarburization in EAFs:

• Train workers on how to recognize and 

avoid unsafe EAF operations associated 

with excess carbon monoxide 

concentrations during decarburization.

• Verify that the off-gas analyzer system 

accurately measures off-gas 

accumulation in the furnace.

• Use off-gas composition analyses to 

control the oxygen injection rate and 

ensure that gas mixtures above “the 

heat” stay well below the lower limit of 

the carbon monoxide explosive range, 

between 12.5 to 74.2 percent.

• Ensure that proper furnace ventilation 

along with off-gas composition analyses 

are used to help control chemical 

reactions in the EAF headspace.

• Do not consider smaller explosions as 

acceptable and immediately investigate 

their cause to modify furnace process 

controls to prevent them.

Figure 1: Pulpit Windows Damaged by

Explosion

Case Study: Near-Fatal Incident

In May 2013, a sudden reaction and explosion 

occurred in a 165-ton capacity EAF that exposed 

three workers on the furnace floor to liquid steel, slag, 

and flames of over 3,000°F that ejected from furnace 

openings. As shown in Fig.1, the explosion was so 

powerful that it broke through the outer explosionproof glass and protective inner windows surrounding 

the pulpit (i.e., control booth). Even though all 

workers wore required PPE, the explosion severely 

burned the three workers on the furnace floor who 

were hospitalized and treated at the regional burn 

center.

Likely Causes of Incident

The employer did not provide adequate furnace 

process controls and allowed unsafe informal 

practices to take the place of written procedures 

established through a workplace hazard assessment. 

The near-fatal explosion occurred when EAF 

operators tilted the furnace and oxygen-containing air 

suddenly entered the headspace. This formed an 

explosive mixture with excess carbon monoxide that 

accumulated in the decarburization process. 

Prior to this incident, sample readings found an 

unusually high carbon content in the hot steel bath. 

As a result, EAF operators began performing an 

extended decarburization process to reduce the carbon 

content to the pre-specified target. The following 

chain of events describes unsafe practices that led to 

the explosion: 

• Initially, some EAF burners were run on high to 

inject more oxygen than usual into the bath at a 

high injection rate, according to this plant’s 

informal routine practice.

• Reactions from this rapid oxygen injection 

generated carbon monoxide at a rate that 

overwhelmed the EAF ventilation system and 

consumed all oxygen in the headspace, creating 

excess carbon monoxide over “the heat” in the 

EAF (instead of the normal furnace process of 

conversion to carbon dioxide).

• Positive pressure in the EAF from the increased 

carbon monoxide concentration also prevented the 

air influx from furnace openings that was 

necessary to replenish the oxygen.

• Flames from inside the EAF headspace escaped 

from furnace openings, indicating that small 

carbon monoxide explosions were occurring inside 

the EAF, but no written procedures existed at this 

plant to monitor or control excess carbon 

monoxide concentrations in the EAF headspace.

• After tilting the EAF, as informal routine practice 

after small explosions, carbon monoxide escaped 

through the slag door and other furnace openings, 

suddenly pulling oxygen-containing air from the 

pouring side into the headspace and causing a 

violent explosion.
How O SHA Can Help

OSHA's On-site Consultation Program offers free and 

confidential advice to small and medium-sized businesses in 

all states across the country, with priority given to highhazard worksites. On-site Consultation services are 

independent of OSHA enforcement and do not result in 

penalties or citations. Consultants from state agencies or 

universities work with employers to identify workplace 

hazards, provide advice on compliance with OSHA 

standards, and assist in establishing safety and health 

management systems. To locate the OSHA On-site 

Consultation office in your state, call 1-800-321-OSHA 

(6742) or visit OSHA's Consultation web page.

O SHA Approved State Plans: Twenty-seven states and 3 

U.S. territories operate their own occupational safety and 

health state plan approved by OSHA. A list of state plans is 

available at: www.osha.gov/dcsp/osp/index.html.

O SHA Compliance Assistance: OSHA’s compliance 

assistance specialists throughout the nation provide 

information to employers and workers about OSHA 

standards, rights and responsibilities under the Occupational 

Safety and Health Act, present short educational programs 

on special hazards and help with other compliance 

assistance resources. Contact your local OSHA office for 

more information by calling 1-800-321-OSHA (6742) or 

visit OSHA's web page at www.osha.gov.

Workers' Rights

Workers have the right to:

 Working conditions that do not pose a risk of 

serious harm.

 Receive information and training (in a language 

and vocabulary they can understand) about 

workplace hazards, methods to prevent harm, and 

the OSHA standards that apply to their workplace.

 Review records of work-related injuries and 

illnesses.

 Get copies of test results that find and measure 

hazards.

 File a complaint asking OSHA to inspect their 

workplace if they believe there is a serious hazard 

or that their employer is not following OSHA's 

rules. OSHA will keep all identities confidential.

 Exercise their rights under the law without 

retaliation or discrimination.

For more information, see OSHA's web page for workers.

Contact O SHA

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.osha.gov, or call OSHA at 

1-800-321-OSHA (6742), TTY 1-877-889-5627.

• Control furnace tilting during EAF 

operations to help avoid creating 

potentially explosive gas mixtures.

How to Protect Workers from Carbon 

Monoxide Explosion Hazards in EAFs

OSHA recommends the following to protect 

workers from explosion hazards in EAFs:

• Ensure that engineering controls (e.g., 

shields or shelters) adequately protect 

workers from maximum potential blast 

overpressure, heat gradients, and struckby hazards from explosions.

• Develop and implement written 

procedures for workers to stand behind 

shields or shelters when on the furnace 

floor or to remain in the control booth, to 

the maximum extent possible.

• Develop and implement written 

procedures to detect and control excess 

carbon monoxide concentrations in the 

EAF headspace.

• Ensure that procedures for alarms or 

signals to workers on the furnace floor 

alert them when potentially hazardous 

conditions occur (e.g., if off-gas analyses 

indicate carbon monoxide buildup).

OSHA also requires employers to ensure 

that workers use PPE that will adequately 

protect against explosion hazards in EAFs 

(see 29 CFR 1910.132(a) and 

1910.132(d)(1)(i)).

For more relevant resources visit OSHA’s 

Scrap Metal Recycling Webpage and 

OSHA’s Basic Steel Products Webpage.