Explosion prevention and protection in the Food Industry

The production of food and beverages in the food industry involves processes in which flammable substances are used, handled or produced in powder form (e.g. flour, sugar, grain, etc.) and in gas and/or vapour form (e.g. ethanol). In addition, the supply of the energy required to carry out these raw material transformation processes may be provided by the use of other flammable substances in the form of gas and/or vapour (e.g. natural gas, hydrogen, etc.).

The risk of explosion is therefore permanently present and with it comes the need to prevent the possibility of an explosion and/or mitigate its consequences. In order to achieve this objective, the main existing international standards establish the performance of an ‘Explosion Risk Assessment’ as one of the main measures. This assessment is carried out by means of the so-called ‘Explosion Protection Document’ or DPCE through the European ATEX Directives or the ‘Dust Hazard Analysis’ or DHA through the NFPA (National Fire Protection Association) standards.

Explosion risk assessment:

A proper explosion risk assessment should determine what explosion prevention and/or explosion protection measures should be necessary to minimise the possibility of an accident with the aim of achieving a safe installation. This should include the use of recognised international standards:

• European standards (EN standards), derived from international IEC standards and reaching those related to the classification of ATEX zones (EN 60079-10-1 and 2), evaluation of ignition sources (EN 1127-1), explosion venting protection systems (EN 14491) and technical reports (CEN/TR 16829 on prevention and protection in bucket elevators).
• VDI standards (German standards), such as those relating to explosion prevention and protection in baghouses and bucket elevators (VDI 2263).
• NFPA standards (American standard), among which we can highlight the one dedicated to the prevention and/or protection against fire and explosion in solid handling industries (NFPA 654), or the one dedicated to the prevention and/or protection against fire and explosion in the agricultural and food industry (NFPA 61).

According to these standards, the steps of a complete risk assessment should be as follows:

Identify the flammable substances used in the process and obtain their explosive parameters (Minimum Ignition Energy, Minimum Ignition Temperature, Minimum Explosive Concentration, etc.), e.g. through direct testing by a certified laboratory or through existing databases (e.g. BIAS GESTIS DUST-EX).
Establish the frequency and duration of the occurrence of an explosive atmosphere according to the process conditions (ATEX zone classification), e.g. by applying EN 60079-10-1 and 2 or VDI standards.
Assess the occurrence and effectiveness of ignition sources in the process (hot surfaces, mechanical sparks, electrostatic discharges, electric sparks, etc.), e.g. by using the EN 1127-1 standard.
Obtain the resulting risk level using existing methodologies (e.g. RASE2000).
Establish the necessary explosion prevention and/or protection measures to reduce the level of risk to a level acceptable to the user, using standards such as CEN/TR 16829 for bucket elevators or NFPA standards.

Recommended preventive and protective measures

In the food industry, there are different processes to which the risk assessment methodology can be applied, among which the following stand out:

• Reception and storage of raw materials: this can be granular materials (barley, malt, maize, etc.) or powdered materials such as flour, sugar, spices, etc.
• Cleaning process: used for granular materials through the use of equipment such as cleaners and screens.
• Milling process: usually used for granular materials through the use of mills.
• Mixing process for powdered materials, for which equipment such as weighing scales and mixers are used.
• Drying process with the objective of decreasing the moisture level of the product: can be used for granular materials or for powdered materials.

The transport of materials between the different processes can be carried out either by mechanical means (bucket elevators, chain conveyors, screw conveyors, etc.) or by pneumatic transport systems (air transport).

In addition, the different existing processes usually have dust extraction systems, either consisting of individual bag filters or small cartridge filters installed directly on the equipment itself.