Seismic Zones: Infrastructure, Equipment, and HVAC

Seismic zones are regions where earthquakes are more frequent, and where accurate cartographic recording is crucial for developing social and urban planning, as well as for adopting risk mitigation measures.

Earthquakes primarily result from the release of energy in the tension zones between tectonic plates (interplate earthquakes). Another cause is volcanic activity and molten material inside the plates (intraplate earthquakes), which, although the seismic magnitude is typically not as high, can have significant consequences due to the epicenter being closer to populated areas.

The main seismic zones of the planet are:

• The Circum-Pacific Zone, one of the areas with the highest seismic intensity, surrounding the Pacific Ocean;
• The Alpine-Himalayan Belt, extending from the Iberian Peninsula and northern Africa to Indonesia;
• The Mid-Atlantic Ridge, which includes the Azores archipelago;
• The Rift Valley Zone in East Africa.

Seismic Risk in Portugal

Portugal and Spain have shown some seismic activity, making them higher-risk zones than most of Europe. According to the Portuguese Society of Seismic Engineering, Portugal, particularly in the southern part of the country and the Azores, is characterized as a zone of significant seismicity due to its location. The region is affected by not only interplate earthquakes but also due to the proximity of the following active faults:

• The Tejo Valley Fault (likely the origin of the 1755 earthquake);
• The Gorringe Fault (the epicenter of the 1909 Benavente earthquake);
• The Azores Archipelago, affected by the meeting of three tectonic plates (American, Eurasian, and African).

Financial Losses and Damages

In areas prone to earthquakes and tremors, proper design and engineering are essential to ensure the stability of buildings. However, earthquakes can affect not only the structure but also non-structural components, such as mechanical, electrical systems, plumbing, and fire protection systems.

When such an event occurs, the main financial impacts are the costs of equipment repair, cleaning the damage, and the loss of the building’s function.

Especially in an industrial building, replacing HVAC equipment, ducts, pipes, electrical systems, and fire network systems can be more expensive than the structure itself, and damaged non-structural elements can make the building unusable.

Seismic protection in HVAC

The ASCE (American Society of Civil Engineers) has building codes and provides guidelines for the seismic protection of non-structural elements through the Minimum Design Loads for Buildings and Other Structures (ASCE 7, 2010 edition).

The ASCE also assigns importance factors to different equipment. In simple terms, the importance factor reflects the severity of a potential failure of the equipment in question. HVAC equipment, smoke removal systems, backup generators in hospitals, and pipes that transport hazardous materials would all have higher importance factors.

The primary purpose of seismic support is to restrict the horizontal shaking of an earthquake. All seismic supports firmly anchor the equipment to the structural elements of a building, allowing them to move with the structure during an earthquake. This prevents the equipment from tipping over, falling from its suspended location, or colliding with other objects.

Seismic Air Handling Units (AHUs) are essential in earthquake-prone areas as they ensure the continuity of HVAC and ventilation systems, minimizing structural and operational risks.

Technical and Safety Requirements for AHUs in Seismic Zones:

1. Reinforced Structures

• AHUs in seismic zones need a more robust structure to withstand vibrational movements without compromising their integrity;
• The use of stronger materials and construction methods helps absorb and dissipate seismic energy, preventing breaks, deformations, or failures;
• Reinforcements on welds and joints maintain the system’s rigidity.

2. Proper Fixation and Seismic Supports

• The fixation of AHUs to the ground or supporting structures should be done using special anchoring elements, such as bolts and mounting plates, capable of resisting multidirectional forces;
• The antivibration supports, commonly found in conventional AHUs, are adjusted to work effectively during seismic events, using dampers and isolators designed to withstand dynamic loads.

3. Vibration Isolation and Damping

• To mitigate the effect of tremors, an isolation system is used that separates the ATU from the building structure, allowing it to move without causing damage;
• Special damping systems help absorb vibrations, preventing the equipment from transferring forces to the building’s structure;
• Base isolators, which allow for some freedom of movement and absorb the energy from the impact, are particularly useful.

4. Seismic Testing and Certification

• Seismic AHUs are tested to meet seismic resistance standards, such as ASHRAE Standard 171 (Seismic Resistance Requirements for HVAC Equipment);
• Vibration and dynamic resistance tests help assess the unit’s resilience and predict its behavior during actual earthquakes.

5. Design Considerations for Specific Contexts

• In critical buildings, such as hospitals, data centers, and industrial facilities, where continuous ventilation is essential, the use of seismic AHUs is indispensable to maintaining operations;
• It is also common to integrate seismic sensors that, upon detecting tremors, automatically adjust the system’s operation to avoid overloading or unexpected shutdowns.

6. Redundancy and Backup in Critical Systems

• Redundant systems are often installed to automatically activate in case of failure or damage to the primary system;
• This ensures ventilation and air control even under adverse conditions, especially in locations with essential functions, such as healthcare areas.

These structural reinforcement and isolation strategies help ensure that the AHU continues to operate or can be quickly restored after a seismic event, maintaining safety and contributing to the environment’s functionality.