This map is not a layout—it is an order for finding hazards
At an integrated steelworks, carbon monoxide (CO) is not merely an incidental pollutant produced by chance. In coke making, it is present as a component of coke oven gas generated when coal is heated without air. In a blast furnace, it is formed by the reaction of coke with the hot blast and serves as a reducing gas that removes oxygen from iron ore. It is a useful fuel within the process, but once it escapes the equipment it becomes an acute poisoning hazard that is difficult to detect by color or odor.
A CO map should therefore not begin by placing a few dots next to equipment names. It must overlay the normal process flow, pressure boundaries, potential leak connections, abnormal release paths, and places where people remain or travel. The map in this article is conceptual; it does not show the actual layout or detector locations of any specific steelworks. An actual detector map must be prepared and validated by qualified personnel using the site’s process safety information, piping and instrumentation diagrams, ventilation and weather data, work routes, incident and alarm history, and field risk assessment.
CO pathways by process at a glance
The conceptual flow can be read as follows.
The coke-plant path runs from coal charging through the coking chambers, standpipes and goosenecks, collecting main, by-product recovery equipment, cleaned-gas piping, and fuel users.
The blast-furnace path runs from top charging and reactions inside the furnace through the top-gas uptakes, dust collection and cleaning equipment, gas holder and mains, hot-blast stoves, and other fuel users.
In both paths, process gas can escape into the work environment at doors, covers, valves, flanges, expansion joints, drains, water seals, instrument connections, purge and vent points, and bleeders.
Gas transported a long distance through piping can create new leak or incomplete-combustion points at boilers, reheating furnaces, hot-blast stoves, and mixed-gas stations far from the equipment where it originated.
The actual point of exposure to released CO is not determined by the source alone. Wind direction, temperature, pressure, gaps in buildings, roofs, platforms, pits, underground passages, and the time people spend there all matter.
The U.S. Environmental Protection Agency’s description of the coke-production process shows how volatile matter generated during carbonization travels through standpipes and goosenecks to the collecting main, then passes through cooling, tar removal, ammonia and light-oil recovery, and desulfurization before cleaned coke oven gas is used as fuel. The agency’s description of the iron and steel production process shows the path in which CO-containing gas recovered from the top of the blast furnace is dust-collected and cleaned, then used as fuel in hot-blast stoves and other processes. Drawing these two paths first helps prevent hazards beyond the point of generation from being overlooked.
Areas to mark in the coke-making process
Charging points and the battery top
When coal is charged, gas generation and pressure changes are substantial during the early stage of carbonization. If charging-hole lids, standpipe caps, goosenecks, dampers, or collecting-main connections are blocked or poorly sealed, raw gas containing CO can leak onto the battery top. The U.S. Occupational Safety and Health Administration’s coke oven emissions standard requires inspection of goosenecks, standpipes, caps, and charging ports before charging and requires gas passages and aspiration systems to be maintained. This means the integrity of the route by which gas flows reliably to the collecting main matters—not merely visible smoke.
On the map, mark the entire battery top as a linear hazard zone rather than as a single point. Distinguish each oven’s charging ports, the row of standpipes, collecting and crossover mains, pressure-control points, and inspection walkways; place work scenarios such as charging, decarbonizing, and opening lids on separate layers. The top is neither always safe nor always hazardous simply because it is elevated. The rise of hot raw gas, lateral transport by wind, and eddies around nearby structures can occur at the same time.
Pusher side, coke side, and oven doors
Oven doors and frames, chuck doors, and cracks are recurring leak points during carbonization. When a door is opened and coke is pushed, process conditions change rapidly while workers and mobile equipment approach closely. Mark the pusher side and coke side separately, and connect door maintenance, cleaning, and sealing work with the cabs of the pusher and guide car, waiting positions, and pedestrian routes.
CO can also form in the pushing, transport, and quenching areas for incandescent coke, depending on combustion conditions and ventilation. The quench tower alone, however, must not be used as a proxy for the battery’s raw-gas leak risk. Charging, leaks during carbonization, pushing, and wet or dry quenching have different causes and time patterns, so the alarm history and work exposure for each must be assessed separately.
By-product recovery and gas-cleaning systems
Downstream of the collecting main are multiple enclosed units, including primary gas coolers, exhausters, tar removers, ammonia recovery, light-oil recovery, and hydrogen sulfide removal. The hazard in this area does not diminish simply because it is far from the ovens. Gas is compressed and conveyed while repeatedly passing valves and pumps, condensate drains, sampling points, manholes, and water seals.
Vessels and piping opened for maintenance, blockage-clearing work, sections purged after isolation, and pressure boundaries upstream and downstream of exhausters should be marked as separate work scenarios. Coke oven gas may contain hydrogen, methane, hydrogen sulfide, and various vapors in addition to CO. A single CO sensor therefore must not be assumed to account for flammability, toxicity, and oxygen-deficiency hazards. The required multigas combination and potential sensor interference should be determined from the actual gas composition and work conditions.
Cleaned-gas mains and fuel users
Cleaned gas may be sent through a gas holder or distribution main to oven heating, boilers, reheating furnaces, or mixed-gas systems. The map must not stop at the coke-plant boundary. Trace the gas throughout its full lifecycle, including holder seals, compressors, control valves, mixing stations, low-point drains, condensate pots, building penetrations, burner trains, and exhaust outlets.
Using different colors for gas that is normally contained and for post-combustion exhaust helps prevent leak detection from being confused with combustion-condition monitoring.
Areas to mark in the blast-furnace process
Top charging equipment and pressure boundaries
Inside a blast furnace, coke reacts with the hot blast to produce CO, which rises through the burden and reduces iron oxides. Top gas containing CO is recovered through the upper uptakes. The charging equipment, bell or bell-less top, pressure-equalizing lines, area around the rotating chute, inspection openings, and seals at the furnace top therefore form the first mapping zone.
Pressure fluctuations during charging, seal wear, blockages, and inspection openings can alter the normal recovery flow. An older blast-furnace health hazard evaluation by the U.S. National Institute for Occupational Safety and Health documented that CO concentrations in blast-furnace gas can be very high. Those values came from a particular historical workplace and are not standards to apply directly to a present-day site, but they clearly show that even a small raw-gas leak can create severe exposure.
Uptake, dust-collection, and gas-cleaning areas
Top gas passes through uptakes and downcomers to cleaning equipment such as a dust catcher or cyclone, wet scrubber, or electrostatic precipitator. Mark the inlet and outlet of each vessel, isolation valves, flanges, expansion joints, pressure gauges and sampling points, drains, and sludge and water-treatment connections. Water in the gas-cleaning area does not mean that CO has been removed. If the main purpose of cleaning is dust removal, CO-containing gas with usable fuel value continues to flow after cleaning.
Water seals and drains are boundaries between the gas and liquid systems. Low liquid levels, blockages, incorrect valve operation, or openings for maintenance can create a path for gas to move into pits or drainage systems. Do not trace only the piping above ground; inspect underground pits, trenches, valve rooms, pump rooms, and wastewater connections as well.
Bleeder, vent, and purge points
A bleeder is equipment for safely relieving pressure; it does not mean the outlet is safe when people are nearby. The UK Health and Safety Executive’s blast-furnace explosion investigation report shows that top bleeders and pressure control are critical boundaries in major-accident analysis. A map should show the discharge direction and operating conditions of bleeders and emergency vents together with remote and field access routes, nearby platforms, and air intakes.
Startup, blow-down, restart, shutdown, abnormal pressure, and nitrogen or steam purging create gas movements different from normal operation. These conditions should be managed with separate scenario maps rather than small annotations on a single normal-operation map. When a release is expected, access control, wind checks, remote monitoring, communications, and evacuation criteria must be linked.
Gas holders, mains, and hot-blast stoves
Cleaned blast-furnace gas moves through holders and large-diameter mains to hot-blast stoves and other fuel users. Hazard points include holder seals, main valves and expansion joints, drip pots, condensate discharge, mixed-gas equipment, hot-blast stove burners, combustion chambers, stacks, and building penetrations. Even an alarm far from the blast furnace should not be dismissed as an unrelated false alarm; trace the connected gas network backward.
Valve sequencing, purging, flame confirmation, and interlock status are important during stove changeover and fuel changeover. Fixed detectors do not replace mechanical integrity, safety instrumented systems, or combustion controls. Detection signals are meaningful when combined with predefined actions such as isolation, ventilation, alarms, and access control.
Cast house and the area around the furnace shell
At the taphole, runners, tapping work areas, and around the furnace shell, potential CO exposure overlaps with hot work, dust, and molten-material hazards. Develop separate scenarios for abnormalities in the furnace shell or cooling system, tapping operations, and leaks from nearby gas piping. Do not exclude lower spaces merely because workers stay there only briefly. Areas with little wind and surrounding structures, locations beneath stairs, cable tunnels, and outdoor-air intakes for control rooms can become pockets or ingress routes.
How to include wind direction and elevation on the map
The U.S. NIOSH CO chemical guide gives CO a relative gas density of approximately 0.97 compared with air. Because this value is very close to that of air, a rule that always places sensors only at the ceiling or only near the floor is inappropriate. Actual dispersion depends heavily on the released gas’s temperature and velocity, ambient wind speed, ventilation, eddies around structures, openings, and pressure differences.
Hot top gas or raw coke oven gas may initially rise through thermal buoyancy. But cooled, cleaned gas discharged horizontally or pressed downward by wind may travel between platforms and buildings. This is why both high locations—such as beneath roofs and canopies and at control-room air intakes—and poorly ventilated low locations—such as pits, trenches, and basements—must be investigated. Choose sampling points based on the anticipated release plume and workers’ breathing height, not on a single elevation.
The map should show not only the seasonal prevailing wind but also real-time wind indicators, local backflow caused by buildings, calm conditions, and the direction of mechanical ventilation. Review each scenario so that evacuation assembly points are not downwind of a potential source. Before work, brief personnel on the current wind and anticipated gas path; if conditions change, access and evacuation routes must be able to change as well.
Design fixed and portable detection together
The role of fixed detectors
Fixed detectors are well suited to continuous monitoring and early warning. Priority candidates include connections with recurring leak potential, pressure boundaries on collecting and distribution mains, gas-cleaning rooms, holders and mixing stations, burner areas, semi-enclosed platforms, outdoor-air intakes for control and electrical rooms, and frequently used walkways. However, one sensor beside a piece of equipment cannot represent the entire area. Because wind and obstacles can carry gas around a sensor, confirm the path to the detector for each scenario.
The UK Health and Safety Executive’s guidance on selecting and using gas detectors explains the distinction between fixed detectors for continuous monitoring and early leak warning and portable detectors for pre-entry checks of confined spaces, leak tracing, and warnings during hazardous work. Fixed-sensor locations should account for the purpose of the alarm, anticipated releases, ventilation, and maintenance access; after installation, use real or simulated tests to verify that gas reaches the sensor.
Do not copy general numbers from this article as alarm setpoints. Review Korean regulations, company exposure limits, sensor range and response time, and the site’s emergency-response philosophy when establishing alarm, warning, and interlock levels. Power loss, communication failure, sensor faults, and over-range conditions must also be distinguishable in the control room. Include periodic calibration, bump tests, transport delay in aspirated sampling lines, filter contamination, and cross-sensitivity in the maintenance plan.
The role of portable and personal detectors
Portable detectors follow the actual breathing zone of people moving between fixed sensors. NIOSH’s workplace CO prevention guidance recommends routine measurements in areas where CO may be present and the use of personal alarms. Personal detectors may be needed by workers performing rounds, collecting samples, operating valves, clearing blockages, tracing leaks, working before and after maintenance, or approaching to investigate an alarm.
Before confined-space entry, test from outside at multiple heights and depths, and continue monitoring throughout entry. One safe reading does not guarantee that conditions will remain safe. Isolation, lockout/tagout, blinds, purging, ventilation, entry permits, attendants, and rescue plans must all be in place. An ordinary worker must not enter a location where high concentrations are possible merely carrying a detector to search for the leak source.
Personal instruments should be function-checked before the start of a shift and calibrated according to the manufacturer’s procedure. Assess whether other components of coke oven gas, including hydrogen, may affect an electrochemical CO sensor, as well as performance under high temperature, humidity, dust, or oxygen-deficient conditions. The equipment becomes an effective protective measure only when workers understand what an alarm means, the direction for immediate evacuation, whom to notify, and the conditions prohibiting re-entry.
Six steps for completing a site map
Using the latest process flow diagrams and piping and instrumentation diagrams, trace CO-containing gas through generation, recovery, cleaning, storage, mixing, combustion, and release all the way to the end of each path.
Separate from normal operation, develop scenarios for charging, pushing, tapping, changeover, startup, shutdown, blow-down, purging, bleeder operation, and maintenance.
In the field, verify leak boundaries such as doors, caps, seals, valves, flanges, expansion joints, drains, water seals, sample points, and temporary hoses.
Overlay worker stations, patrol routes, control rooms, air intakes, elevated platforms, pits, underground passages, evacuation routes, and assembly points to assess potential exposure.
Apply wind direction and speed, thermal buoyancy, ventilation, structural eddies, and seasonal changes to select fixed-detector candidates and a portable-monitoring plan, then perform gas-reach testing.
When an alarm activates, verify responsibilities and timing through automatic and manual isolation, ventilation, announcements, access control, evacuation, rescue, and authorization for restart.
The final review questions are simple: Where is the gas generated? Where does it flow? At which boundaries can it escape? Where will wind and structures carry it then? Who will be exposed first? Which detector provides warning, and when? What happens automatically or manually after the alarm? Every unanswered box is an item for further investigation, not a location for one more sensor.
Operating principles more important than the map
When a CO alarm occurs, workers should not remain to check for symptoms; they must immediately leave by the designated route and notify the control room. Following site procedures and real-time wind direction, move crosswind or upwind to a safe area, and prohibit untrained personnel from attempting rescue alone or re-entering. Entry into high-concentration or unknown-concentration atmospheres is work for trained personnel equipped with appropriate respiratory protection and a rescue system.
A good CO map is not merely a sensor location plan; it is a living process-safety document. Review the map after equipment changes, piping bypasses, fuel changes, building additions, ventilation changes, recurring alarms, leak incidents, or changes to work routes. Actual detector placement cannot be finalized without a site-specific risk assessment and field testing. A conceptual map helps ensure that questions are not missed, but it cannot measure the site’s pressure, gas composition, weather, structures, or people.