service heat treating

When a load hangs up during quenching, seconds matter and improvised decisions can escalate risk. In this Technical Tuesday installment, Bruno Scomazzon, general manager of Precision Heat Treat Ltd., outlines a step-by-step emergency response procedure for exactly this scenario, which is one of the most dangerous in atmosphere heat treating. Drawing on real-world experience, this guide is intended to help companies develop their own effective procedures for maintaining safety, controlling furnace conditions, and coordinating with emergency responders in high-risk situations.

This informative piece was first released in Heat Treat Today’s February 2026 Annual Air & Atmosphere Heat Treating print edition.

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Scenario Overview

A load has been transferred to the quench and the elevator is lowering into the oil, but the load becomes hung up and fails to fully submerge. The inner door successfully closes, and the outer (front) door remains closed.

This is an extremely high-risk situation requiring strict adherence to emergency procedures. The goal is to protect: first the personnel (minimize the chance of injury or escalation of the situation), then the facility, and finally the equipment.

1. Immediate Actions

DO NOT Open Outer Door

There may be a natural urge to assess the situation but resist temptation. DO NOT stand in front of or directly beside the outer door and never open it during an active hang-up. Opening this door can introduce oxygen to a hot chamber, causing:

• Explosions or flash fires.
• Loss of containment due to door warping or mechanical failure.

In extreme cases, the outer door may be compromised (blown off, stuck open, or partially open) with visible flames. This warrants immediate escalation to the fire department.

If Outer Door Cannot Be Closed

In this scenario, immediately notify the fire department and advise them to prepare for a foam response. DO NOT allow the use of water. This may trigger violent reactions with oil or atmosphere and spread the fire!

Internal trained responders should:

• Don PPE.
• Retrieve fire suppression gear.
• Be ready to protect critical systems until responders arrive.

DO NOT shut down the furnace.

2. Maintain Electrical Power

To ensure essential systems stay active, you must maintain electrical power. Ensure these systems stay active:

• Set the furnace cycle to manual mode from auto mode. This will bypass any PLC sequencing from auto cycling doors, elevators, and handlers.
• Keep the pilots lit.
• Keep the oil cooler running to prevent tank overheating.
• Shut off oil heaters to prevent additional heat loading in the quench tank.
• Keep quench agitation on low during the entire period to assist in lowering the temperature at the interface surface area between the hot load and the oil. This prevents stratification and dissipates radiant heat into the oil.
• Keep the recirculating fan running.
• Keep the instrumentation functioning for monitoring.

NOTE: Loss of these systems eliminates visibility, atmosphere control, and safe response options.

3. Atmosphere Management

Maintain a protective atmosphere and positive furnace pressure to prevent oxygen ingress and uncontrolled combustion:

• Set the carbon control to “0”.
• Shut off the enriching gas.
• Shut off the ammonia.
• Shut off the dilution air.

Nitrogen Purge

These steps depend on whether a nitrogen purge is available; it is highly advised that nitrogen purge be available for all IQ or straight through units. Be sure you understand how long it takes for your specific furnace to fully purge endothermic gas. While NFPA 86 recommends five volume turnovers, some experts advise planning for up to ten per hour in an emergency. Each furnace should have established purge data under normal conditions so operators can act with confidence when time is critical.

• Begin a nitrogen purge immediately (if available) and maintain it throughout the event.
• Use at least the minimum flow rate specified in your documentation. If safe, higher flow may be used to help displace flammable gases from the heating and quench chambers.
• Maintain furnace temperature at 1500°F during the purge.

Residual pockets of Endo gas may remain trapped in less ventilated areas. If the chamber temperature drops below the ignition point before all flammable gas has been displaced, the introduction of oxygen could trigger an explosion. In some cases, trapped Endo and pressure imbalances can lead to sudden releases (“furnace burp”), where oil or gas is expelled due to internal pressure buildup.

After the Purge

The goal of the nitrogen purge is to displace Endothermic gas with an inert atmosphere while maintaining elevated temperature to assist in burning off residual flammable gases and preventing dangerous mixtures. This process must ensure positive pressure throughout the furnace.

• A purge followed by plunge cooling in nitrogen is a valid approach if the purge is verifiably complete.
• Depending on furnace size and cooling rate:
• Larger furnaces may cool slowly enough for a complete purge.
• Smaller or faster-cooling units may require a brief temperature hold before controlled cooling or plunge cooling.

NOTE: Once the hung-up load cools to a safe temperature (~150°F), perform a standard shutdown.

Without Nitrogen (in Endo)

If there is no nitrogen purge, or it is insufficient, the only option is to let the hung-up load cool in the vestibule while continuing to burn Endo and maintain the furnace temperature at 1500°F. Once the vestibule/oil tank cools below 150°F and the danger has passed, initiate a standard furnace shutdown.

4. Safety Management

• Alert the local fire department immediately. If the situation becomes unmanageable, or if there is any doubt about the ability to maintain control, evacuate the facility and wait for trained professionals. The safety of plant personnel is paramount.
• Notify plant safety and site management.
• Evacuate all non-essential personnel from the heat treat area.
• Inform all departments that a high-risk incident is in progress.

Fire departments are most effective when they are familiar with your facility before an emergency occurs. Make sure they know the layout of your operation, including:

• Oil tank locations and sizes
• Electrical panels
• Gas shutoffs
• Hot zones

5. Controlled Cooling Period

• Maintain atmosphere protection throughout the event.
• DO NOT open doors until the vestibule’s temperature is low and stable.
• Cooling time will depend on load mass and heat retention. Expect five or more hours.
• Use furnace pressure stability, effluent observations, and gas behavior as indirect temperature indicators.

6. Load Recovery Procedure

• Once cooled and stabilized, perform a standard shutdown, starting with the removal of endothermic gas if applicable.
• DO NOT attempt manual load removal until the system is verified safe.
• Only maintenance personnel may retrieve the load, using PPE and appropriate tools.

7. Fire Department Familiarization

Every facility should build rapport with the local fire department before an emergency ever happens. Schedule annual walkthroughs and identify the following:

• Number of furnaces
• Quench oil tank volumes
• Hot zone and live panel locations
• Emergency shutoff points

Stuck doors are commonly caused by failed pneumatic valves. Shutting off and bleeding compressed air may allow the mechanism to reset. Always consult your equipment manual or the manufacturer before attempting corrective action.

The fire inspector conducting walkthroughs is not the one coming to fight your fires — train the ones who are.

8. Post-Incident Protocol

Before returning the furnace to service:

• Conduct a formal investigation.
• Identify and correct root cause(s).
• Document all key parameters and actions taken.
• Re-train operators as needed.

Furnace Signage

An operator is likely to read your safety plan but may forget a vital protocol during an emergency. Having bold, brightly colored warnings printed and posted at the panel that the operator can remove and use in an emergency can be invaluable.

Final Reflections

We cannot predict every consequence. No procedure can account for every possible variable in a live emergency. Once an event is in motion, all we can do is respond with the best judgment, training, and intentions — always with the safety of people as the highest priority.

This document is intended as a working reference: a structured reference developed with care, real-world experience, and best practices. It is not a one-size-fits-all solution, but a tool to help teams create or enhance their own effective procedures and respond adaptively in high-risk situations.

Fire preparedness is essential in every heat treating facility. Fires happen, and they are not always small. It is critical to know when to act, when to evacuate, and when to call for help. Equipment manuals provide a foundation, but preparedness through training and planning is the best defense.

Acknowledgments: The author would like to thank Daniel H. Herring, “The Heat Treat Doctor,” The HERRING GROUP, Inc., and Avery Bell with Service Heat Treat in Milwaukee for their valuable input.

About The Author:

Bruno Scomazzon is the general manager of Precision Heat Treat Ltd. in Surrey, British Columbia, Canada, with over 40 years of experience in metallurgical processes and heat treating operations.

For more information: Contact Bruno at bruno@precisionheattreat.com.