Novel Micro-structures for Fire Escape Masks

Abstract

Residential fires in the UK claim over 400 lives annually and cause nearly 21,000 deaths worldwide, presenting a deadly combination of heat, smoke, and toxic gases. Escaping such scenarios, particularly in multi-story buildings, can be a daunting challenge. Fire escape masks serve as a potential lifeline by supplying 15 minutes of clean, breathable air. The masks adsorb and break down harmful toxic gases emitted by fires and filter out hazardous soot particles. However, limitations include increased breathing effort, costly or underperforming catalysts and an inability to ensure safe air temperatures for users. This PhD explored these limitations to enhance the protection offered by fire escape masks.

Novel routes for structuring adsorbents were examined to reduce inhalation burden and enhance mask accessibility. Extruded phenolic carbon monoliths were compared to commercially utilised granular carbons to establish a performance baseline. Monolithic carbons demonstrated great potential to reduce pressure drop (92 % lower), while achieving similar adsorption metrics for VOCs (1000 ppm n-butane at 1 L min−1) compared to best performing granular carbons (0.109 g g−1 uptake, 21.3 min g−1 breakthrough). However, the monoliths experienced instant breakthrough, potentially compromising filter safety.

A 3D-printed approach was utilized to create unique activated carbon structures, addressing the issue of immediate breakthrough. Micro-channelled polymer structures were successfully produced and optimised. The pyrolysed prints displayed desirable characteristics, including high carbonization yields (up to 35 wt%), and significant BET surface areas (1065 m2 g−1) after a 40 - 50 wt% activation. Good geometrical accuracy was maintained throughout printing and pyrolysis. Notably, tessellated hexagonal and spiral channels performed best, achieving comparable breakthrough times (21.1 min g−1 and 21.8 min g−1 respectively) to the monolith and granular baselines, while exhibiting no instantaneous breakthrough. Tessellated hexagonal microchannels showed an 82 % lower pressure drop, while the spiral design showed a higher resistance to instantaneous breakthrough at high flow rates.

Nano-structured tricobalt tetroxide was explored as a promising catalyst for low temperature oxidation of carbon monoxide to increase the cost-effectiveness and stability of the filter catalysts. A novel reflux synthesis method most consistently produced nano-rod structures, giving an exceptional catalytic activity of 21.3×10−7 mol g−1 s−1. This surpassed the performance of baseline commercial catalysts (4.67×10−7 - 12.5×10−7 mol g−1 s−1) and, after supporting, was suitable for incorporation into a fire escape mask.

Incorporating thermal sinks remains an unexplored aspect in fire escape masks, yet plays a crucial role in countering elevated air temperatures and safeguarding the respiratory system from burns. Two promising materials, a shape-stable phase change material (PEG-based) and a lithium hydroxide salt, were investigated. The lithium salt demonstrated excellent heat storage density (1219 - 1459 J g−1), however, a high dehydration temperature (70 to 90 ◦C) rendered it unsuitable. PEG-based phase change materials exhibited an optimal temperature range and achieved reasonable heat storage density (up to 115.4 J g−1). The PEG material was structured via die casting into 3D printed moulds, reducing heat storage enthalpies when tested in-line (48.6 J g−1) but still displaying sufficient heat removal for safe escape.

In summary, this research investigated methods to enhance fire escape masks. A prototype filter was proposed in the conclusions, capturing the main PhD findings. An granulated bed of structured cobalt nano-particles utilises the high inlet air temperature to increase activity and fully protect against carbon monoxide. A fabric filter then captures harmful particle sizes in the air. Following this, a structured phase change material (using PEG held in a polymer matrix) reduces the air temperature to safely breathable levels, additionally enhancing the adsorption performance of the following 3D printed, activated carbon microchannels to fully remove toxic volatile carbon compounds.

Date of Award	11 Oct 2023
Original language	English
Awarding Institution	University of Bath
Supervisor	Semali Perera (Supervisor), Andrew Burrows (Supervisor) & John Chew (Supervisor)