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Important FAQs

 

Did you know…

There are many factors to be considered when a project or specification lands on your desk with a requirement for a Blast Resistant Building. Details such as the PSI rating and blast duration are only the beginning of the information needed to accurately design and fabricate these structures. We have compiled the following information to help our clients gain a better understanding of application requirements that must be considered when designing these critical life safety structures.

We hope this information proves to be worthwhile and educational, and that you will gain a higher understanding of the many critical design factors that must be considered to produce a resilient blast resistant building that can satisfy your particular needs.  Thanks for your valuable time, and know we look forward to working with you on your current or upcoming applications.

 

Exterior Wall Deflection:

   
Equipment Mounting is a critical consideration in Blast Resistant Buildings
Exterior wall deflection is often overlooked but is a critical factor of consideration when designing a blast reisistant building
Before a blast resistant building RFQ is issued, it’s important to know whether equipment will be installed on the interior surface of an exterior wall, or if equipment, furniture or other fixtures will be placed in close proximity to the interior surface of an exterior wall, especially if the wall faces the potential source of a blast event.  This is an important detail that can be easily overlooked and yet have potentially lethal consequences.

Many manufacturers engineer some or all blast rated wall systems the produce to “flex” during a blast event.  This form of design minimizes construction costs while preventing permanent wall deformation.  The building thus attains an economically desired response level rating.  However, the consequence can be dire when the surface of a wall moves several inches in the blink of an eye, regardless of whether the wall then returns to its original position.  This type of dynamic “diaphragm” action is commonly seen in buildings featuring corrugated wall structures, although plate steel wall systems may also exhibit this characteristic, depending on plate thickness and reinforcement beam spacing and size.

The problem is easy to predict.  Any objects mounted to or placed against the interior surface of an exterior wall inside such buildings may be dislodged or displaced by the instantaneous and violent motion of the exterior wall in such buildings during a blast event.  These objects then become potentially lethal projectiles within the occupied space.

Imagine if you will the effects of a large bookcase, wall mounted electronic device or office desk being catapulted across the work space of a control room or other occupied space.

As you can easily envision, these objects would cause great bodily harm or death to occupants, and would nullify the protection you thought afforded by the building's response rating.  Therefore, regardless of whom you select to furnish a blast resistant building, it’s extremely important to consider this highly critical factor.

The only way to circumvent this issue is clear.  Exterior walls must be designed to minimize or prevent diaphragm action if equipment will be installed on their interior surface, or if equipment, furniture or other fixtures will be placed in close proximity to them.  This is achievable, but comes at a more significant cost.  Otherwise, no objects should be mounted to or placed in close proximity to the exterior walls.  As a buyer, the factor of occupancy may also be considered, but the potential liability for injury or death must be assumed by the buyer, so calculated considerations to ensure the safety of your workforce is essential.   As you will discover, most but not all manufacturers are capable of achieving this level of design, but many pre-engineered, pre-certified or rental fleet structures may not feature this level of integrity.

IMPORTANT NOTE:
As observed both by our Third Party Engineers and Bebco in competitive quoting situations, some manufacturers do not disclose this fact in writing to their clients, nor in some cases do they warn against placing objects on or in close proximity to wall surfaces which are subjected to Reflective Pressure or Overpressure pressure during a blast event, as further described below.  We therefore present this information in collaboration with our third-party engineering associates in the interest of providing complete disclosure to all who may specify, purchase and occupy such structures.

 

PSI Rating:

The PSI Rating for Blast Resistant Buildings is critical, and must be specified as either Reflective Pressure or Overpressure
This critical design factor is the one requirement most clients have readily available when requesting a quotation.  Essentially, the PSI rating is the anticipated pounds per square inch of pressure that a building surface will be subjected to in the event of a blast or cataclysmic event.

In most circumstances, the PSI rating of the wall facing the potential blast source will be higher than all other surfaces, but all walls, the roof and the floor of elevated buildings are subject either to reflective pressure or overpressure which occurs on surfaces not directly exposed to a blast event. 

  These effects of Overpressure occur during the return of atmosphere to the blast source, moments after the initial event.

If the epicenter of a blast event is unknown, or if it may emanate from multiple locations around a blast resistant structure, it may be necessary to rate all walls, the roof and the floor of elevated structures with the same PSI pressure rating. However, any ability to accurately specify the anticipated pressure that may be applied to each individual side and the roof of a blast resistant building can be used to "economize" the structure's design.
 

Blast Duration:

The duration of a cataclysmic event is a critical factor for the design of a blast resistant building
This information is most typically provided in milliseconds, and defines the length of time that a structure may be subjected to a blast event at the aforementioned pressure rating. 

In some applications, since either the duration of time is unknown or the critical nature of the building's intended purpose is extremely critical, the duration of the blast event may be considered as sustained. In these instances, the building must be designed to withstand a continual force.
  As you may already be aware, all manufacturers of blast rated buildings are subject to the same requirement to have accurate information regarding the pressure and duration of a cataclysmic event. The calculation is often extremely complicated, involving the consideration of numerous factors and scenarios, and in the end the calculation may be subjective at best.

However, all factors related to the proper design and manufacturing hinge on these two critical factors, so it is essential that proper calculations be made before the process of specifying a structure of this type is initiated.
 

Pressure Type:

Pressure type is defined as either Reflective Pressure or Overpressure, and is an extremely critical element of design.
This is a description that must follow all PSI ratings and is expressed most commonly as either Reflective Pressure or Overpressure.  From an application standpoint, this description is extremely critical to the design of a blast resistant building. As a basic explanation of the term, Reflective Pressure is the direct force of a blast wave as applied to any wall or roof surface facing a blast force. The terms "on-side" "side-on" or "incident side" pressure is also used to define this particular force on a blast resistant building. Reflective Pressure will be the greatest degree of force applied to a blast resistant building, and its effect can only be minimized by deflection, if a wall or roof surface is more parallel with as opposed to perpendicular to a blast event.

Overpressure is defined as the pressure caused by a shock wave over and above normal atmospheric pressure, which all other sides of a structure will be subjected to during a cataclysmic event. To further define this pressure, understand that a significant shift in air pressure during a blast even has both positive and negative effects, as the atmosphere is “pushed” by a shock wave that first emanates from a source and then returns to the source, much like a wave crashing ashore and then receding back to the ocean.
  The initial emanating shock wave may have little effect on any wall, roof or exposed floor surfaces not directly facing a blast force, but both the emanating and returning shock waves will apply Overpressure forces equal in most cases to at least one-half of the Reflective Pressure.

As an example of how critical these terms are, if a client requests a specific PSI rated building, but does not clarify the pressure type, the safest tendency for manufacturers would be to assume that rating as Overpressure. However, if Overpressure is mistakenly stated as or assumed to be Reflective Pressure, the building's structural integrity will be dramatically inadequate. Depending on when or if clarifications are made, this can either create extreme increases in manufacturing cost or subject occupants to potentially lethal consequences. In conclusion, a proper definition of pressure type is critical, and extreme care should be taken when transferring such information to a manufacturer.  Should you receive information that does not specifically reference these critical terms, you should demand further clarification. In the end, lives can depend on this issue, so please insist as we do in absolute clarity of meaning.
 

Response Levels:

Response Levels determine not only the condition of a blast resistant building after a cataclysmic event, but also determine if occupants may survive the event!
Response levels help determine the condition of a structure after a blast or cataclysmic event. These levels are important to understand, particularly if a structure is used as a safe haven during an emergency situation. The following levels (as enhanced by Bebco for clarity) have been established by the American Society of Civil Engineers (ASCE) committee for the design of Blast Resistant Buildings in Petrochemical Facilities (2010 ed.):
  • Low Response: Localized component damage is anticipated.  The building may be re-occupied, however repairs are required to restore integrity of the structural envelope.  Total cost of repairs is moderate.

  • Medium Response:  Widespread component damage is anticipated. The building should not be re-occupied until repaired. Total cost of repairs is significant.

  • High Response:  Key components may have lost structural integrity and the building may collapse after a catastrophic event due to environmental conditions (i.e. wind, snow, rain).  The building should not be re-occupied.  Total cost of repairs approaches replacement cost of the building.
 
IMPORTANT NOTE:
As observed both by our Third Party Engineers and Bebco in competitive quoting situations, some manufacturers will quote a high response level, if this factor is not specified by the potential buyer. This tactic is applied in order to provide the most competitive bid possible, but can greatly skew the range of competitive bids. You should therefore always clearly state a response level and insist on details regarding this factor if a response level is not specifically listed in writing in response to your RFQ.
 

Door Design:

Bebco utilizes blast resistant door manufacturers that provide complete certificaitons
Another key component of blast resistant building design relates to the doors and framing.  Based on required door function, acceptance guidelines have been classified into 4 categories by the ASCE committee for the design of Blast Resistant Buildings in Petrochemical Facilities (2010 ed.):
  • Category I: The door is to be operable after the loading event and established design criteria for stress, deflection, and the limitation of permanent deformation have not been exceeded. A ductility ratio of 1.0 or less (elastic range) and a door edge rotation of 1.2 degrees should be specified. This category should be specified when the door may be required to withstand repeated blasts or when entrapment of personnel is of concern and the door is a primary exit to the building.

  • Category II: The door is to be operable after the loading event but significant permanent deformation to the door is permitted. A ductility ratio in the range of 2 - 3 and a door edge rotation of 2.0 degrees is recommended. The door must remain operable and this category should be specified when entrapment of personnel is a concern.
 
  • Category III: Non-catastrophic failure is permitted. The door assembly remains in the opening. No major structural failure occurs in the door panel structure, the restraining hardware system, the frame or the frame anchorage that would prevent the door assembly from providing a barrier to blast wave propagation. However, the door will be rendered inoperable. A ductility ratio in the range of 5 to 10 and a door edge rotation of no greater than 8 degrees is recommended. This category should only be specified when entrapment of personnel is not a possibility.

  • Category IV: Outward rebound force and resulting hardware failure is acceptable.
 

Engineering Certification:

An overview our our blast resistant building engineering philosophy and hyperlinks to sources for all applicable standards.
For more information regarding the design of blast rated buildings please visit our Engineering Certification page, for an overview of our engineering philosophy, our methodology for attaining blast rating certifications and convenient hyperlinks to sources for all applicable standards.
   
   

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