Spray drying is a process which transforms a liquid to a powder. The liquid is pumped, and a liquid mist is created through nozzles or atomizers. The mist is then dried by hot gas (mainly air in the Food and Beverage industry).
A spray dryer is a very large and expensive piece of equipment that typically operates 24/7. It is an assembly of a drying chamber, fluidized bed, and separation devices
such as cyclonic equipment or bag house dust collectors.


Spray dryers present explosion AND fire hazards due to the processing of combustible dust. Loss of this type of equipment could result in a long period of business interruption and the replacement cost of the
equipment is high.
The use of spray dryers has increased significantly over the last ten years in the food industry, especially in the dairy sector.


On a Saturday, around 9pm the amperage increases for a pump motor used to rotate the atomizer that transforms the liquid into water mist. As the amperage is surveyed
and reported in the control room, the operator received the information. The control room operator observes that the amperage increases from 129 A to 139 A in a short
period of time.
Some moments after this observation, a fire and an explosion are reported by the alarms and the deluge sprinkler system is manually activated by the operator.
The fire brigade is called and arrives on site 20 minutes later. Since the call to the fire brigade, the fire has spread into the building and has generated significant smoke. The fire has also spread to the cyclonic equipment.

During the following six hours, the fire brigade fought a relatively small fire but with many difficulties due to:
• The height of the building (more than 30 meters with
several catwalks, mezzanines and intermediate floors)
• The electrical shutdown
• The night time


•The building is damaged, including the foundation, intermediate catwalks/mezzanines, metal structure and roof.

• The spray dryer equipment has significant damage. The discoloration of the metal on the different equipment leads our experts to believe the metal structure has
been impacted by the heat of the fire.

• All external equipment such as electrical cabinets have been destroyed

• Although the property damage appeared to be significant and the equipment didn’t collapse, a technical expert has been requested after the cleaning and secure operations. In the following weeks, the different experts and the client have tried to identify if the process could start on a limited capacity based on the client’s need to restart operations as soon as possible.

• After the cleaning and replacement of some equipment, such as electrical cabinets and ducts, replacement of the roof and wall siding begins. The process is restarted but quality controls are not adequate. The client and AGCS chose to replace most
of the spray dryer equipment, including the atomizer, the heating devices, the drying chamber, the fire protection system and two cyclonic separators. The work on site takes more than eight months and the spray dryer starts to produce 12 months after
the event.


After the loss investigation, it was confirmed that the atomizer was not secured well, which caused metal friction and then sparks. An explosion occurred and generated
flames that started a fire involving the combustible powder located in the bottom of the drying chamber.
It was confirmed that the explosion also created a fire inside the premises as the vents were not ducted outside.
The conditions needed to create an explosion are:
• Combustible load – explosive dust, in this case the milk powder
• Containment – confined area, in this case the drying chamber
• Dust suspended in air
• Oxidant – Oxygen
• Ignition source
• The ignition source was the only condition that was missing within the drying chamber to generate an explosion.


• The fire brigade had an adequate water supply for fight the fire but had difficulties to fight the fire.
• The first emergency team has responded the fire and explosion events with effectiveness as the monitoring of the amperage of the pump and other equipment
has correctly informed the operator that something wrong was happening. On the other hand, the process has not been stopped.


Property Damage:
• The deluge sprinkler system installed reduced the damage and prevented collapse of the equipment.
• The presence of vents, even if not ducted outside has avoided the blast of the equipment, which could have created even more damage.
Business Interruption
• The management of the plant has been very proactive.
• The client has a very strong network of plants in the country and has immediately planned the transfer of the raw materials to back-up plants.
• At the same time the client has immediately reactivated an old spray dryer to produce a similar powder even if at reduced capacity.
• For these reasons, the Business Interruption has been limited to approximately a one year period even if some additional costs have been incurred to restart
some equipment.


• Keep in mind that explosion are often followed by fire in spray dryer processes. Explosion is not the only hazard to take into account when you plan to protect
your assets. Some loss prevention rules and protection systems may limit the severity of a fire or an explosion at a spray dryer location.
• Duct adequately designed vents outside of the building. If not possible, install flameless explosion venting or chemical suppression.

• Whatever information is used to monitor the safety of the process, keep in mind that three levels of alarms are needed:
–– First level: The operator must immediately check the effected equipment (i.e. presence of smoldering powder, vibration of the atomizer or the bearing of
the fans, etc.). The operator should have enough time to perform inspections and proceed with a normal shutdown when necessary.
–– Second level: The operator must immediately stop the process according to the normal shutdown procedure (e.g. water on the feed). After shut down,
the effected equipment must be inspected.
–– Third level: The process must be automatically shut down by the emergency procedure, and if the deluge sprinkler system has not already operated
automatically, the system should be activated manually by the operator.
• Install a fire protection system that can be automatically and manually activated with an adequate and reliable water supply.
A good way to avoid the spreading of the fire or the explosion from one piece of equipment to another is to install a rotary feed valve which acts as a stop point,
preventing an explosion or a fire from propagating backwards into the spray drier or vice-versa.
Emergency and organization
• Write an emergency response plan and update on an annual basis with an adequate organization and establishment of the leadership.
• A fire drill should be conducted annually to identify difficulties on site.
• Ensure the effectiveness of the emergency team through a well-organized and well-documented training program. Keep in mind that it is too late to develop skills at the time of an emergency.


Nicolas LOCHET
Regional Technical Manager
Allianz Risk Consulting
+33 607 798 412
Reference LL 13/18/12

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