Publication Date

5-2022

Date of Final Oral Examination (Defense)

3-11-2022

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Mechanical Engineering

Department

Mechanical and Biomechanical Engineering

Supervisory Committee Chair

Erin Mannen, Ph.D.

Supervisory Committee Member

Trevor Lujan, Ph.D.

Supervisory Committee Member

Krishna Pakala, Ph.D.

Supervisory Committee Member

Safeer Siddicky, Ph.D.

Abstract

Background

Over the last 30 years, 83 infant fatalities (113 reported, 30 incidental) directly involving crib bumpers have been reported to the Consumer Product Safety Commission. Of these reports, 90% are for infants under a year old, with 61% occurring for infants between 1 and 4 months of age (Safety, 2020). There are currently a few regulations governing the design of crib bumper products, but none test the suffocation risk associated with these products using biofidelic methods.

Goals

We sought to explore the development of new testing methods that can determine the safety of different products and are physiologically representative of this age range. These test methods were derived from the British Standard BS 4578:1970, Test for Hardness of, and for Air Flow Through Infant Pillows, and further developed through application of medical literature and anthropometric measures.

Methods

In the process of modifying BS 4578:1970, airflow tests and firmness tests were developed and conducted. In airflow testing, we modified the original flowrate to 2 L/min to model a 2 to 4-month-old and examined the effects of increasing probe complexity to be more representative of an infant’s airway system. We sought to find the simplest probe that maintains physiologically representative results for ease of implementation. We also conducted force vs. displacement testing and characterized products based on stress relaxation.

Results and Discussion

We found that a simple model made of a 3-inch diameter hemisphere with two 3.125-mm air channels representing the nares was the best suited for our criteria. This probe was able to distinguish between safe and unsafe product categories, recording mean pressure values of 0.254 ± 0.019 in. H2O and 2.038 ± 0.417 in. H2O respectively. These higher values fit with the expected initial pressure in an infant’s esophagus during occlusion (3.74 ± 1.96 in. H2O) (Cohen and Henderson-Smart, 1986). This led to a recommendation for a threshold to be developed at 0.311 in. H2O for airflow testing. Our firmness testing was able to characterize the different product categories, finding that each category retained a certain percentage of the initial applied force. The most meaningful data to come from this testing was finding the linear relationship between applied force and measured pressure at levels above 2 N, particularly for the traditional products. All R-squared values for this category were above 0.98.

Conclusion

Our goal in this project was to explore the creation of a new and simple testing standard that can be applied to infant sleeping products. We were able to develop a threshold in airflow testing that can differentiate between safe and unsafe products, while showing that our model is physiologically representative. However, it can currently only be shown that this threshold is applicable to crib bumpers and new thresholds may be developed for different product categories. We also found the relationship between force and pressure for the specific products tested, which can allow for approximations of pressure readings under varied loads.

DOI

https://doi.org/10.18122/td.1925.boisestate

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