Is High Response Acceptable for Blast-Resistant Modules?

When choosing a blast-resistant modular building, it is important to understand the term “response level”. We usually assume everyone is familiar with this term and knows what it means, but this is not always the case. Let’s take a closer look at response levels, as the difference between a low response blast-resistant building and a high response one can make the difference between life and death.

Considering response as damage

The response level terminology can be somewhat confusing. One may assume that a building with a ‘high response’ rating would stand up well to a blast and, thus, offering a high level of protection. However, in reality, the opposite is true. In fact, a ‘low response’ rating gives the highest level of protection against blast.

Therefore, when talking about response levels, it is generally a good idea to replace the term ‘response’ with the term ‘damage. When doing so, it becomes clear that a ‘low damage’ (low response) building offers more protection than a ‘high damage’ (high response) building.

Response level ratings have been established by the American Society of Civil Engineers (ASCE) to predict the extent of damage and resources required to repair a building, after withstanding an explosion. The ASCE descriptions of the three response ratings include:

  • Low response: Localized building/component damage; building can be used, however, repairs are required to restore the integrity of structural envelope; and the total cost of repairs is moderate.
  • Medium response: Widespread building/component damage; building cannot be used until repaired; and total cost of repairs is significant.
  • High response: Building/component has lost structural integrity; building may collapse due to the environmental conditions; and total cost of repairs approaches replacement cost of building.

Considering the above definitions, substituting the term ‘response level’ with ‘damage level’ will provide you with an instant picture of what each rating means in terms of damage, repair and safety. Considering the damage and risks of a high response rated building, you will likely prefer a low response or medium response blast-resistant building for your facility.

What to look for when choosing a blast-resistant building

Even though a high response level building can be considered ‘blast resistant’, such a building could sustain significant structural damage during an explosion, and may also collapse, resulting in injuries or even fatalities. We recommend using low or medium response rated blast-resistant modular buildings in areas where there is a risk of explosion in your oil, gas, petrochemical or other similar facility.

There are several companies providing blast-resistant buildings of various designs. However, only a few of the blast-resistant building designs available on the market received a low response rating from ASCE. The most important aspect of a blast-resistant modular building is the safety of your people and assets. All RedGuard Specialist Services blast-resistant modular building designs have been awarded low or medium response ratings, depending on the different blast pressures.

What makes our buildings safe?

The most significant aspect of our buildings’ engineering and design is the placement of steel studs 28cm to 30cm apart, rather than meters apart. This denser stud framework design is similar to a rib cage, which springs back after taking a punch. Similarly, by placing too much flat wall surface between studs, the response level rating rises quickly.

What regulations are in place?

Even though there are stringent international health and safety standards and regulations present in various industries, particularly in the oil and gas industry, there is still no official regulation covering the requirements related specifically to blast-resistant modular buildings.

As the technology in blast resistance is still relatively new, this situation could change. So, at the moment, the closest industry criteria in place are the recommended practices (RP) prepared by the American Petroleum Institute (API). These RP cover both permanent and portable structures located in blast zones and aim to meet specific PSI and duration requirements for placements of buildings in specific zones.

In this regard, API RP 752 covers the management of hazards related to the location of process plant buildings, while API RP 753 covers the same topic, but for portable buildings. These two recommended practices provide guidelines on recommended blast ratings, ensuring that occupied buildings protect people and equipment against blast. As these design considerations cover only two out of three vital criteria, many manufacturers meet the required pressures and durations for specific zones, but incorporate a high response level in their design, making these buildings still at risk of significant damage.

Blast testing

Even with these important guidelines in place, there is no other certification to ensure a building can withstand a blast; proper field testing should be done. To demonstrate that our blast-resistant modular buildings are safe, RedGuard completed a field test, using an explosive charge of 2.7 tons of ammonium nitrate/fuel oil (ANFO) at a standoff distance of 52 meters from the buildings, creating a large explosion. A building design that could sustain only minor damage in this type of explosion would exceed the ratings required to meet ASCE low to medium response standards.

The entire process was filmed by a high-speed camera and after reviewing the footage and closely examining the building’s interior, exterior and structure, they determined the damage. The result was no structural damage to the building, as well as no damage to the furnishings, office equipment, or the crash test dummy placed inside the building. In fact, RedGuard still uses this building at their headquarters.

While blast pressure is a key component of the design formula of blast-resistant buildings, it is the combination of the pressure with the duration and response level that can tell how a blast-resistant building will hold up to an explosion. Therefore, it is important to review response level ratings and the field test results before you choose a blast-resistant modular building. In any case, we want to make sure you understand that a high response blast-resistant building is not an acceptable solution for a blast area in your facility.

At RedGuard Specialist Services, we manufacture only modular buildings that we would use ourselves. If you want to protect your people and assets, you should ask yourself, “Is a high response rating good enough?” If you plan to invest money in a blast-resistant building, take your time to learn more about blast resistance in the guide prepared by RedGuard, the industry leader in blast resistance. In the guide there is an in-depth look at blast-resistance and the things you should know and consider before you buy a blast-resistant building. You can also read our article about the five key considerations when choosing a blast-resistant module.

To find out more about blast-resistant buildings and response levels discussed here, you can also read our technical article or talk to one of our experts.