Article Overview
Shutdowns and turnarounds can create temporary H₂S risks as equipment is depressurized, opened, purged, drained, or taken out of service. This article explains why shutdowns and turnarounds require a different hydrogen sulfide management approach and outlines how temporary emissions control, gas monitoring, treatment planning, and field coordination support safe and compliant maintenance activities.
Why Do Shutdowns and Turnarounds Create Higher H₂S Risk?
Planned maintenance changes how sour gas, hydrocarbons, and process fluids move through a facility. Equipment that normally operates as a closed system may be isolated, depressurized, drained, vented, or opened for inspection. These activities can release H₂S from piping, vessels, tanks, separators, or trapped process fluids.
Dissolved H₂S may also move into the gas phase when pressure falls, liquids are transferred, or equipment is opened. Residual hydrocarbons, sludge, or produced water can continue releasing vapours after the main process stream has been removed.
Before work begins, operators should identify where H₂S may remain, where it could be released, and how those emissions will be controlled before personnel enter the work area.
What Should Be Included in an H₂S Management Plan?
A shutdown or turnaround H₂S management plan should reflect the equipment being taken out of service and the maintenance work being performed. A standard production treatment setup may not be suitable once flows become intermittent and temporary vent points are introduced.
Important planning considerations include:
- Expected H₂S concentration and total gas volume
- Equipment isolation and depressurization sequence
- Temporary vent and purge locations
- Nitrogen or other purge gas requirements
- Gas monitoring points around work areas
- Temporary H₂S treatment equipment and chemical supply
- Worker access, exclusion zones, and emergency response requirements
- Final gas testing before equipment is opened or entered
Reviewing these details before work begins helps ensure the required equipment, chemicals, monitoring devices, and personnel are available.
How Is Temporary Emissions Control Used During Maintenance?
Temporary emissions control may be required when sour gas is released while equipment is depressurized, purged, cleaned, or prepared for inspection. Instead of discharging untreated vapours directly from a vent point, operators can route the gas through temporary treatment equipment.
H₂S scrubbers are commonly used for defined gas release points because they create a contained treatment location before discharge. This is useful during vessel depressurization, pipeline purging, tank venting, and similar maintenance work.
For a real-world example of temporary emissions control during maintenance, see our case study on Turnaround and Shutdown Solutions. During a Central Alberta turnaround, AMGAS treated multiple vacuum truck venting streams containing H₂S and high hydrocarbon concentrations using a dual-phase scrubbing system. The system was supported by continuous onsite monitoring and operational support, allowing emissions to be controlled as work progressed across different parts of the turnaround. The project demonstrates how temporary treatment equipment can help reduce harmful releases, protect workers, and avoid downtime or delays during complex maintenance activities.
When Are Chemical Scavengers Useful During Shutdowns and Turnarounds?
Chemical scavengers may be used when H₂S remains dissolved in residual hydrocarbons, produced water, or other liquids that must be transferred, stored, or disposed of during maintenance.
H₂S scavenger solutions can support liquid treatment where sufficient chemical contact, mixing, and reaction time are available. Treating the liquid phase can reduce the H₂S available to flash into vapour later, although gas phase controls may still be required.
For a broader comparison of chemical, scrubbing, and system-based methods, read our article Hydrogen Sulfide Treatment Methods: What Works and When to Use Them. This article explains how different treatment methods are selected according to H₂S phase, concentration, flow conditions, and operating requirements. During shutdowns and turnarounds, that comparison is especially useful because residual liquids and temporary gas releases may require different treatment methods at different stages of the maintenance process.
What Does H₂S Management Look Like During a Real Turnaround?
Consider a gas processing facility preparing a separator and connected piping for internal inspection. The unit is isolated and depressurized, but residual sour liquid remains in low points and the vessel continues releasing H₂S as pressure falls.
The maintenance team routes the separator vent through a temporary scrubber, establishes continuous gas monitoring around the work area, and treats residual liquid before removal. Nitrogen is then used to purge the system, with displaced gas continuing through the treatment equipment until testing confirms acceptable conditions.
This approach controls H₂S at several stages and gives the team clear verification points before the vessel is opened.
How Can Operators Maintain Safe and Compliant Conditions During Maintenance?
Safe shutdown and turnaround work depends on coordination between operations, maintenance, HSE personnel, contractors, and treatment specialists. Changes in sequence, gas volume, equipment condition, or H₂S concentration should be communicated quickly because they may affect the treatment plan.
Monitoring should continue through depressurization, purging, draining, and equipment opening. Temporary treatment equipment should also be checked as conditions change to confirm flow and H₂S loading remain within the expected range.
What Should Operators Understand About H₂S Management During Shutdowns and Turnarounds?
Shutdowns and turnarounds require a flexible H₂S management strategy because process conditions, release points, and treatment needs change as equipment moves from normal operation into maintenance. Effective planning should account for residual gas and liquids, temporary venting, purging, emissions treatment, monitoring, and safe work sequencing.
When these controls are planned together, operators can reduce exposure risk, support compliance, and maintain safer conditions throughout maintenance activities. For facilities preparing for shutdown or turnaround work, AMGAS can help assess temporary H₂S treatment requirements and identify a practical approach for the planned maintenance scope. Use the form below to contact our team and discuss an H₂S management plan for your next shutdown or turnaround.