Why Analysis Begins Before Calculations
In design practice, a significant source of errors in explosion protection is often not the calculation procedure itself, but an incorrectly defined event scenario that the procedure is intended to describe.
This is particularly relevant to industrial facilities where the explosion hazard results from a combination of the technological process, the properties of the substances being handled, and the geometry of the building. In such cases, explosion protection cannot be considered merely as the selection of a single solution, such as an explosion venting area. It must form part of a broader analysis covering the development of the event and the response of the entire facility.
Potential origins of an explosion include process equipment such as dust collection filters, silos, mills, or conveying systems. However, the point of initiation does not always correspond to the actual extent of the effects. An explosion may propagate through process connections, ducts, pipes, or other pathways capable of transferring flame and pressure to subsequent parts of the facility. Designing industrial buildings at risk of explosion therefore requires a combination of knowledge in process technology, explosion protection, and structural engineering.
From the structural designer’s perspective, it is therefore essential not only to determine the parameters of the phenomenon itself, but also to understand how the resulting action will be transferred to the building and how the entire structural system will respond.
Several levels of analysis must be distinguished in the design process. Explosion parameters of a substance describe the ability of a mixture to generate a particular phenomenon. Explosion protection parameters, such as P_red, describe the effectiveness of the protective measure applied. For the structural designer, however, the key issue is to determine the action that will ultimately be transferred to the facility and how the structure will respond to that action.
This distinction is particularly important because the value of an explosion protection parameter is not directly equivalent to the structural load. Between the hazard analysis and the assessment of the building lies the stage of translating the results of the explosion analysis into an actual model of structural behaviour.
Therefore, explosion protection design should not begin with the question:
“What venting area should be provided?”
but with the question:
“What explosion scenario may occur, and what action will be transferred to the specific facility?”
Only a correctly defined scenario allows appropriate protective measures to be selected and structural safety to be assessed properly.
The explosion venting area is the result of the event analysis, not the starting point of the design process.
This article focuses on issues related to the deflagration of combustible dusts and flammable gases and vapours in industrial facilities. It does not cover structural design for the effects of detonations of explosive materials, nor does it constitute a complete explosion protection design methodology.
Explosion Scenario and the Actual Extent of the Effects
Once the objective of the analysis has been established, the next stage of the design process is to define the explosion scenario. The assumed scenario determines the scope of the subsequent analysis, the selection of explosion protection measures, and the method used to assess the action on the structure.
In industrial facilities, the point at which an explosion is initiated is not always identical to the area affected by its consequences. The development of the phenomenon depends on the properties of the combustible substance, the configuration of the process installation, the geometry of ducts and pipes, and the potential for flame and pressure propagation between individual items of equipment and building spaces.
This is particularly important in dust extraction systems and combustible dust conveying systems. A primary explosion in equipment such as a dust collector may propagate to other parts of the installation and, in the absence of effective protective measures, into the production hall. In addition, damage to equipment may result in the release and dispersion of deposited dust, creating conditions for a secondary explosion.
This example illustrates a scenario in which the explosion is not effectively confined to the process equipment. As a result of flame or pressure propagation, deposited dust in the hall may become suspended, potentially leading to a secondary explosion. Even a thin layer of deposited dust can form a cloud with a concentration within the explosive range and involve a significant part of the building volume. It is precisely this type of scenario that can generate actions relevant to structural design.
For the structural designer, the concept of the actual area affected by the explosion is therefore of key importance. This area is not defined solely by walls, floors, or the functional subdivision of the building, but by the potential for the effects of the explosion to be transferred between individual parts of the facility.
The boundaries of the area under consideration should therefore not be determined solely by the architectural subdivision of the building. A building partition does not necessarily constitute an actual boundary of the effects if flame and pressure can propagate through process ducts or other connections between spaces. Process ducts, conveying pipes, service openings, or inadequately protected penetrations may result in spaces that are formally separated in the design documentation effectively forming a single system from the perspective of explosion propagation.
The application of explosion protection measures to a particular process does not necessarily mean that the consequences of an explosion will be confined solely to the protected process installation. Experience from industrial accidents shows that, under certain conditions, the effects of an explosion may also extend to adjacent equipment and structural elements of the facility. Therefore, when defining an explosion scenario, it is necessary to consider not only the protected equipment, but also the potential development of the event beyond its boundaries and the resulting consequences for the structure, human safety, and the continued operation of safety systems. Systems responsible for evacuation and fire protection, such as emergency lighting, fire alarm systems, smoke extraction systems, or fire suppression installations, may also be damaged, potentially hindering evacuation and rescue and firefighting operations.
At the same time, any extension of the scope of the analysis should result from the actual mechanism of explosion development rather than from an assumption that the entire facility must be considered exposed to the explosion hazard. The application of appropriate measures to limit propagation can significantly change both the assumed scenario and the scope of the subsequent analysis.
From Explosion Scenario to Structural Action Model
Defining the explosion scenario makes it possible to identify the area affected by the event and its anticipated development. This does not, however, mean that a load model suitable for direct use in structural calculations is already known at this stage.
Explosion analysis primarily describes the development of the physical phenomenon and the effectiveness of the protective measures applied. Structural design, by contrast, requires determination of how the action is transferred to the load-bearing elements of the building. Moving from one stage to the other requires engineering interpretation that takes into account the nature of the action, structural detailing, and the actual load-carrying behaviour of the facility.
The action generated by an explosion is not transferred to the entire load-bearing system simultaneously. Building envelope elements are loaded first, followed by secondary structural elements and their connections, and only then by the main structural frame. The way in which forces are transferred depends on the geometry of the facility, the explosion protection measures applied, and the interaction between individual structural components.
For this reason, the assessment of structural safety should not be limited to checking individual members. It is essential to determine how local damage may affect the behaviour of the entire structural system and whether the structure retains the capacity to redistribute loads and maintain stability.
Particular attention should be paid to elements responsible for the three-dimensional integrity of the structure, such as bracing, connections, and components ensuring continuity of the load-bearing system. Damage to such elements may lead to a change in the structural system and an increase in the extent of damage, even where the explosion action itself is local.
The action model adopted for structural calculations should therefore be based not only on explosion parameters, but above all on an analysis of how the action is transferred through the individual components of the building. Only a model defined in this way provides an appropriate basis for the design of protective measures and the assessment of structural safety.
Explosion Venting in Buildings – From Calculation Results to a Design Solution
Once the structural action model has been established, the next stage of the design process is the selection of measures intended to mitigate the effects of an explosion. One of the most commonly applied solutions is explosion venting, which is intended to provide controlled discharge of explosion products and limit the pressure rise within the protected space to the level assumed in the design.
Explosion venting can be designed using methods set out in standards such as EN 14491 for dust explosions. These methods allow the required venting area to be determined for specified boundary conditions. The result, however, always relates to a specific explosion scenario and a specific space covered by the analysis.
The calculated venting area alone therefore does not constitute a complete design solution. It is also necessary to verify whether the proposed solution can be correctly implemented in the actual facility and whether its operation will be consistent with the assumed event scenario.
The venting area is therefore the result of analysing the assumed explosion scenario, rather than an independent design objective. Its value cannot be considered separately from the area affected by the explosion, the explosion protection measures adopted, and the structural behaviour model.
In design practice, factors such as the location of venting devices, the direction of discharge of explosion products, the impact on the surroundings, and interaction with the building structure must also be taken into account. A venting element does not operate independently of the facility. In many cases, it forms part of the building envelope and affects both the venting process and the way in which the resulting action is transferred to the primary structure. This applies in particular to lightweight roofs, curtain walls, and dedicated explosion vent panels and relief hatches.
Explosion venting design therefore requires close coordination between explosion analysis and structural analysis. The explosion protection specialist determines the effectiveness of the proposed solution in relation to the assumed explosion scenario, while the structural designer assesses its influence on the behaviour of the building and the safety of its load-bearing elements.
The importance of explosion venting is also reflected in national technical building regulations. In Poland, § 221 of the Regulation of the Minister of Infrastructure of 12 April 2002 on the technical conditions to be met by buildings and their location contains specific requirements for rooms presenting an explosion hazard. Among other provisions, it requires a lightweight roof above such a room unless the required explosion-relief capacity is provided by appropriately selected explosion protection devices, such as relief diaphragms, hatches, or glazed openings made of ordinary glass, with a total area meeting the requirements specified in the regulation. The regulation also requires walls separating a room presenting an explosion hazard from other parts of the building to withstand a pressure of 15 kPa. These requirements are specific to Polish building regulations and should not be interpreted as requirements arising directly from the ATEX Directives. For projects in other countries, the applicable national or local building, fire-safety, and technical regulations should always be reviewed, as they may contain additional or different requirements concerning explosion venting, structural resistance, and the separation of rooms presenting an explosion hazard.
It is also worth noting that the glazed openings made of ordinary glass referred to in the Polish regulation are not equivalent to modern glazing systems used in industrial buildings. Contemporary façades are constructed using various types of glass and curtain wall systems whose behaviour during an explosion may differ significantly from that assumed for traditional ordinary glass. For this reason, explosion venting is most commonly provided by dedicated explosion vent panels or relief hatches with known opening characteristics that can be taken into account in the design analysis.
The Role of the Structural Designer in the Explosion Protection Design Process
The structural designer should become involved at a stage when the solution can still be developed, rather than only during final verification. Decisions concerning the event scenario, the extent of the area included in the analysis, the method of explosion venting, and the adopted action model may directly influence structural behaviour. Structural assessment should therefore not be treated as the final stage of the process, carried out only after the process and explosion protection assumptions have already been finalised.
The core tasks of the structural designer include:
- assessing which elements of the facility may be subjected to the anticipated action,
- determining how loads are transferred to the load-bearing system,
- identifying elements that are critical to three-dimensional stability,
- assessing the consequences of potential local damage,
- coordinating protective measures with structural requirements.
Of particular importance is the translation of explosion analysis results into structural design assumptions. Parameters obtained from the explosion protection analysis must be interpreted in relation to the actual facility: its geometry, load-bearing system, connections, and the behaviour of individual structural elements.
Collaboration between the process engineer, the explosion protection designer, and the structural engineer helps avoid situations in which a solution is correct from the perspective of one discipline but creates problems in another area of the design.
The role of the structural designer is therefore not limited to checking an individual member. It also includes assessing whether the entire facility will maintain the required level of safety under the assumed action scenario.
The best solutions are achieved when process analysis, explosion protection design, and structural design are carried out in parallel from the beginning of the design process rather than being brought together only at the final verification stage. The structure is not an add-on to the explosion protection system. It is an integral part of it and must be designed with consideration of the actual development of the event.
Conclusions
Designing explosion protection for industrial buildings requires the integration of process hazard analysis, the selection of explosion protection measures, and the assessment of structural response to anticipated actions.
The foundation of a proper design process is the correct definition of the event scenario. It determines the extent of the area covered by the analysis, possible propagation paths, and the subsequent assumptions relating to protective measures and the structure. Even correctly performed calculations will not produce an appropriate solution if they are based on an incorrectly defined design case.
Explosion parameters of substances, operating parameters of protective systems, and actions adopted for structural assessment describe different stages of the same process and cannot be treated as interchangeable values. The key issue is the translation of explosion analysis results into an action model corresponding to the actual behaviour of the building. This stage of engineering interpretation forms the bridge between hazard analysis and structural design.
The safety of a facility does not result from the application of a single protective measure or from achieving the required venting area. It is the outcome of a coherent design process in which the event scenario, explosion protection measures, and the structure are analysed as interrelated elements.
Explosion protection design does not begin with calculating the venting area or checking the load-bearing capacity of an individual structural member. It begins with understanding how an explosion may develop in a specific facility and what action will actually be transferred to the structure.
Only such an approach makes it possible to develop a solution that not only complies with applicable standards and satisfies the relevant design criteria, but above all reflects the actual development of the event and ensures the safety of the facility as a whole.
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Author: Sebastian Słaboszewski
Bibliography
- EN 1990 – Eurocode – Basis of structural design.
- EN 1991-1-7 – Eurocode 1. Actions on structures – Part 1-7: General actions – Accidental actions.
- EN 1127-1 – Explosive atmospheres – Explosion prevention and protection – Part 1: Basic concepts and methodology.
- EN 14491 – Dust explosion venting protective systems.
- NFPA 68 – Standard on Explosion Protection by Deflagration Venting.
- Polish Regulation of the Minister of Infrastructure of 12 April 2002 on the technical conditions to be met by buildings and their location.
- ASCE/SEI 59 – Blast Protection of Buildings.
- API RP 752 – Management of Hazards Associated with Location of Process Plant Buildings.
- Clough R.W., Penzien J. – Dynamics of Structures.
- Eckhoff R.K. – Dust Explosions in the Process Industries.
- Baker W.E., Cox P.A., Westine P.S., Kulesz J.J., Strehlow R.A. – Explosion Hazards and Evaluation.
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