Novel Airbag Inspired Explosion Suppression System for Mitigation of VAM Explosions

This report encompasses outcomes from a multi-phase program aimed at the development of a swift explosion suppression system for the mitigation of VAM explosions. To address the rapid suppression of gas explosions, a novel technology was proposed, named RAINBOES (Rapid Action Inflating Nitrogen Bag Obstruction Explosion Suppression). A prerequisite is that the airbag must be inflated within 1 s to securely block the tube, thereby stopping the flame from further propagating.

Phase I of the program, conducted in 2021-2022, focused on the proof-of-concept and small-scale prototype development and carried out the following activities:

• Adapting the key features of the current generation of automotive airbag systems in developing and advancing the RAINBOES concept;
• Developing different RAINBOES design configurations;
• Performing CFD (computational fluid dynamics) simulation to examine the performance of the designs/configurations devised in scenarios relevant to VAM abatement;
• Prototype development based on selected designs/configurations.

Phase II of the program consists of two parts (Part-I and Part-II) and deals with the demonstration of the reliability of the technology at scale:

• Part-I: simulation of airbag working mechanism for larger VAM capture duct with diameter ranging from 1m - 8.5m using single or multiple airbags.
• Part II: Conceptual design of an experimental setup (duct) to assess airbag performance in large-diameter ducts.

In Phase II, Part I, the Finite Element Analysis (FEA) was employed to examine the inflation process of the airbag in a typical duct with a circular cross-section. The simulation involved testing the obstruction of ducts using both single and multiple airbags across a range of diameters (1 to 8.5 m). The simulation outcomes were promising, demonstrating the effectiveness of the airbag concept. Hence, it stands as a viable fire and explosion mitigation solution for largescale industries such as underground coal mining.

The following findings have been achieved from the simulation work. The minimum air mass flow rate required to securely block the tube depended on the tube size, following a power-law function;

• Using a single airbag, it can rapidly and completely block an approximately 4.5 m diameter duct in less than 1 second;
• As the tube size increased, the internal pressure and energy density decreased even after the airbag had been fully inflated. A high air mass flow rate is beneficial in achieving a high internal pressure;
• Using multiple airbags (4 airbags, for instance) can rapidly and entirely obstruct a 8.5- meter diameter duct in less than 1 second.

In Phase II, Part II, a conceptual skid-mounted duct has been designed to support future experimental investigations of airbag performance in large-diameter ducts, similar to those used in coal mine ventilation systems.

The design incorporates a range of sensors to measure pressure and air velocity. Additionally, the air movement within the duct, both before and after airbag activation, will be visualised and captured using a smoke generator and two high-speed cameras: one mounted perpendicular to the duct and the other positioned at the outlet along the flow path. A total of 8 connection ports is included for the installation of airbags, allowing flexibility in the number, size, and positioning of airbags used during testing.

The airbag inflating system consists of a compressed air reservoir and a series of quick-acting valves that release air into the airbags for rapid deployment. The entire operation, including the smoke generator, sensors, cameras, and inflating system, is controlled via a synchronised program to ensure precise coordination and data collection during testing.