Introduction
The smooth running of a facility is essential for productivity and consistent output. But there are many reasons a business may need to shut down a process. These can include inspections, maintenance, equipment installation, or scheduled closures such as holiday periods or end-of-day routines. Of course, each shutdown is followed by a startup.
These transition periods are among the most hazardous stages within a process. Equipment can be used in new ways, human error becomes more likely, and risks can quickly escalate if procedures are not followed. The moments before you start or stop a process are when vigilance matters most.
Why Startup and Shutdown Are Risky
The hazards linked to startup and shutdown can be grouped into two categories:
Startup Hazards
- New or modified equipment may be more likely to fail
- Hidden hazards from installation or design are uncovered
- More people are involved, which increases potential exposure
- Human error is more likely due to inexperience, time constraints, or management pressure
- Introduction of hazardous materials for the first time
- Process start-up conditions may be different to operating conditions
- Temporary equipment such as isolations may have been used
Shutdown Hazards
- Incorrect or inappropriate isolations
- Redundant or ancillary equipment left online
- Equipment malfunction, inactive sections, or incorrect setpoints
- Inadequate identification of connected ‘live’ plant
A mismanaged startup or shutdown can escalate quickly, leading to fires, explosions, or environmental damage. This is often when teams believe the plant is at its safest.
How to Ensure Safe Startup
To maintain safe operation, several key steps must be followed during startup.
It is essential to ensure that all safety, operating, maintenance, and emergency procedures are established and well understood by your team. Training must be thorough and include people at all levels of the business involved in the process, including maintenance teams who may encounter additional risks during early operation.
Next, the equipment itself must be verified. All new or modified equipment must meet design specifications, and any changes should be assessed for additional hazards. This is also the stage where risk assessments help uncover potential failure points and hazards that may not be visible during normal operation.
Knowing what could go wrong, and what to do if it does, creates a safe startup for everyone involved in the process.
Pre-Startup Safety Review
A Pre-Startup Safety Review (PSSR) is one of the most important steps in ensuring a safe transition into or out of operation. Mandatory under OSHA’s Process Safety Management (PSM) standard (29 CFR 1910.119(l)), the PSSR verifies that equipment, procedures, documentation, and training are complete and appropriate before a process is restarted or shut down. This final check confirms modifications, maintenance, or system changes have been correctly implemented and nothing has been overlooked. Critically, it should confirm that any outstanding actions from risk assessments have been completed satisfactorily.
Startup and shutdown are times when systems are most vulnerable. During startup, equipment goes from idle to fully operational. This can sometimes happen under conditions that haven’t been fully tested. Even small issues can create serious problems when systems are first brought online.
Shutdown carries similar risks, with temporary configurations, abnormal operating conditions, and increased manual intervention creating more risk of error. A PSSR ensures these conditions have been anticipated and controlled. It checks that safeguards are functioning, all critical steps have been completed, and all workers understand the actions they are required to take.
Whether returning to service or coming offline, a PSSR helps catch last minute errors, reinforces good operational discipline, and provides confidence that the system is ready for a safe transition.
Organisations that lack the internal resource to conduct rigorous PSSR-style checks consistently may benefit from a Comprehensive Safety Review, where a dedicated competent person provides the structured, independent oversight needed to catch issues before they escalate.
How to Ensure Safe Shutdown
Shutting down a process safely requires the same level of attention and discipline.
Checklists are one of the most effective tools for ensuring safe shutdown. They provide a structured, step by step guide that teams can follow to verify each action has been correctly completed before moving on to the next. Whether they involve routine tasks or manual operations, checklists help build a culture of consistent, reliable safety practices.
A shutdown checklist might include confirming all isolations are correctly placed and locked out/tagged out, draining, venting, or neutralising reactive chemicals as needed, and inspecting valves, hoses, and lines for leaks or wear.
Teams should then confirm that isolations are in place and that valves and controls are set correctly. Ancillary and redundant equipment must also be handled appropriately.
Throughout the shutdown, strong, continuous communication between operators, maintenance, and engineering teams is essential. Inspections should be carried out as hazards may emerge that are not visible during normal production.
Human Factors and Operational Pressure
Human factors play a major role during startup and shutdown. Pressure from management to complete these transitions quickly can cause miscommunication, potentially leading to rushed decisions or skipped steps.
Although speed is beneficial for reducing downtime and enhancing productivity, it can have a huge impact on safety and significantly increase the risk of an incident. Teams need the time, focus, and support to follow procedures properly. Even a small distraction at this stage can turn a minor oversight into a major incident.
Real life incidents
Hickson & Welch Limited (1992) – Jet Fire
During routine maintenance on a distillation column still base containing nitrotoluene residues, an ignition occurred around 1:20 PM. This triggered an incandescent conical jet fire (described as a 200 ft horizontal and vertical jet of burning vapors) that erupted from a manhole. The jet propelled the manhole cover like a projectile, severely damaging the site’s control building and impacting an adjacent office block, igniting multiple internal fires.
How could this be prevented?
Ensuring the distillation column was fully purged and free of reactive residues before maintenance, verifying isolation and gas-free conditions, and using strict hot-work and confined-space controls, including continuous atmospheric monitoring, would have prevented the ignition and resulting jet fire.
BP Amoco Polymer (2001) – Catch Tank Incident
Workers were trying to open a vessel containing partially reacted plastic as part of the startup process when the vessel unexpectedly blew off due to high pressure levels. This ejected hot plastic and formed a vapour cloud that ignited and killed three people.
How could this be prevented?
Using clear, updated shutdown/startup procedures, performing a thorough Pre-Startup Safety Review (PSSR), and ensuring gas monitoring and effective communication would have prevented the toxic release.
Terra Industries Fertiliser Plant (1994) – Explosion
Ammonium nitrate solution was left in vessels during the shutdown process. As a result of this, when steam was applied during routine startup activities, acidic conditions and a lack of monitoring led to a runaway reaction, creating an explosion.
How could this be prevented?
Ensuring all reactive materials were removed before shutdown, carefully monitoring temperature and pressure during startup, and training operators on chemical hazards could have prevented the runaway reaction.
Dupont Belle (2010) – Chemical Plant Release
During the shutdown process of a phosgene unit, workers disconnecting lines noticed a burst hose releasing phosgene gas, which is highly toxic. Tragically, a supervisor died after inhaling the gas.
How could this be prevented?
Replacing or inspecting flexible hoses, using proper line isolation before disconnection, and implementing gas monitoring with protective equipment would have prevented the phosgene release.
Best Practices and Tips
When approaching a startup or shutdown, several best practices help ensure a safe and controlled process:
- Use PSSR-style reviews, even for minor or seasonal shutdowns and startups.
- Clearly assign roles and communicate responsibilities across operators, maintenance, engineering, and safety teams.
- Prioritise safety critical actions first, with non critical tasks following only once the process is confirmed safe.
- Document lessons learned during each startup or shutdown for continuous improvement.
- Build a safety first culture, where safety is valued above speed or convenience.
Conclusion
Safe startup and shutdown are essential for protecting people, equipment, and the environment. By planning ahead, using structured procedures such as PSSR, and ensuring strong communication, businesses can significantly reduce the risks associated with these critical stages.
Following proper procedures may take more time, but it prevents accidents, avoids costly downtime, and protects your workforce.
Sigma-HSE helps organisations implement structured, compliant startup and shutdown practices so every operation begins and ends safely. Get in touch to find out more about our Process Safety Management solutions.
