Biofidelic Considerations for Improving Standardized Airflow and Firmness Testing for Infant Sleep Products
Authors: Davis Wyatt D. 
Published: September 2022

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.