Catalyst change outs

What is a catalyst and what are catalyst change outs?

A catalyst in the chemical industry is a substance that speeds up a chemical reaction without being consumed itself. Catalyst materials need to be changed when the old catalyst becomes contaminated and/or less active over time.

Catalysts are needed for certain chemical reactions. Petroleum refining is a good example of this. As the catalyst material becomes contaminated over time and loses its effectiveness, a reactor is stripped of some of the catalyst material it contains. This is called reactor unloading. The reactor is then cleaned, inspected, repaired where necessary and reloaded with new catalyst material; the overall procedure is called a catalyst change out. The plant is temporarily taken out of service for all this work.

Unloading can be done in various ways. In some cases, the catalyst can flow out through discharge openings; this is called dumping. Catalyst material also remains in these cases. To remove this, someone enters the reactor. Their work involves loosening the catalyst material with a shovel, a jackhammer or other tools. The operative then sucks up the material with a strong vacuum hose or lets it flow out of the reactor through the outlets into a separate receptacle. In some cases, instead of dumping, all catalyst is removed by vacuum suction by entering.

Dangers of a catalyst change out

Explanation of an inert atmosphere

The catalyst material to be unloaded may have acquired pyrophoric or self-heating properties over time. That means that the catalyst material spontaneously ignites on contact with oxygen. The reactor must be opened to unload the remaining catalyst material. This is done by entering the reactor. The oxygen percentage in the reactor must be lowered to prevent the catalyst material from igniting. This is done by filling the reactor with a non-combustible gas such as nitrogen before entering. This is called inertisation. In this low-oxygen environment (inert environment), it is not possible to breathe without appliances and a supply of breathing air is required for the person entering the reactor. This person is called the diver.

Suffocation

If someone who enters the reactor with this inert environment encounters breathing difficulties, they will be in mortal danger due to the lack of oxygen.

Burying

The catalyst material may shift under the influence of gravity. Catalyst material often consists of pellets. In a reactor, some of those pellets are often stuck together to form hard lumps in the form of pillars or caked against the wall. These chunks can come loose unexpectedly, fall apart and land on the diver. The diver could become buried under this catalyst material. Burying can lead to direct injuries such as bruises and fractures and becomes a serious issue at the point when the diver cannot free himself independently if he is under a larger layer of catalyst material. Dumping catalyst material while the diver is still present in the reactor increases the risk of burying. As catalyst material flows away, already formed pillars can become unstable and topple over.

Combustion

Combustion can occur when someone is buried under catalyst material. The air exhaled by the diver enters the reactor through valves on the underside of their helmet. This exhaled air still contains about 16 per cent oxygen. Inertising the reactor with nitrogen therefore does not prevent increased oxygen levels in the vicinity of the breathing helmet. In a situation where a diver is standing on the layer of catalyst material, this increased oxygen content does not pose a problem. The exhaled air mixes directly with the nitrogen gas in the reactor and barely contributes to the oxygen percentage in the reactor. However, this becomes problematic if the exhaled breathing air comes into direct contact with the contaminated catalyst material, as in the case of someone being buried in that material. In that case, the contaminated catalyst material may ignite. Being buried may cause the helmet to leak, causing the breathing air to escape and reach the catalyst material in the reactor.

Type of companies where catalyst change outs take place

The companies that carry out catalyst change outs with inert entries are mainly refineries. This is also done at a number of companies that produce hydrogen as an intermediate or end product.

Zeeland Refinery accident

On 3 February 2023, a hired employee died in an accident at the Zeeland Refinery site. This happened during the removal of catalyst material from a reactor. In this incident, the diver in the reactor with an inert atmosphere was buried in catalyst material. Oxygenated air was released from his breathing helmet, which came into contact with the catalyst material lying on top of him. As a result, the catalyst material ignited. A rescue was launched, but nothing could be done for the victim after he was taken out of the reactor.

There have been previous fatal accidents during catalyst change outs under inert atmosphere n Germany (Linge 2014), Finland (Porvoo 2021) and France (Le Havre 2021).

OVV report: lessons and recommendations

The Dutch Safety Board (OVV) investigated the incident. The report was released in April 2025: Stop using divers in low-oxygen environments to unload reactors (Dutch Safety Board).

The report provides 3 lessons for the industry and all employers involved:

1. Stop unloading reactors by means of inert entries.
2. Develop new, safer ways of unloading reactors.
3. Share information on accidents (and near-accidents) within the industry.

The report makes specific recommendations to the companies concerned.

Legal framework

The refining sector and other affected plants where catalyst change outs are carried out with the combined risks of asphyxiation, combustion and intoxication are covered by the Seveso Directive and/or the ARIE scheme. The Netherlands Labour Authority monitors this under the Major Hazard Control (MHC) programme.

Supervision of catalyst change outs

In 2026, inspectors from the Netherlands Labour Authority will conduct company visits. The aim is to assess the extent to which the industry has moved, or is moving, to other practices to carry out the catalyst change outs safely. Special focus will be placed on the unloading, the method used to remove the catalyst from the reactor.

The use of current and alternative practices is assessed on the basis of how the employer demonstrates that it controls the hazards of burying and combustion without any new hazards being introduced.

If the industry focuses on preventing inert entries, a safer way of performing the catalyst change out will come about.