Failure analysis of several exercise balls that exploded during use causing serious injury

1. Why Some Exercise Balls Explode
& Others Do Not
Duane Priddy and Tom Peeler
Plastic Failure Labs

2. Imagine what would happen to this man if the ball he was placing his
weight on suddenly exploded!
I have worked as an expert on two matters Involving the explosion of a
fitness ball while athletes were lifting a 100 lb weight in each hand
during training. Both ended up with shattered bones in their arms and
months of excruciating pain and rehabilitation.

3. What Makes Balls Burst Resistant?
Flexible PVC foam
structure which interrupts
fracture propagation

4. Importance of Wall Thickness Uniformity

5. How Fitness Balls are Manufactured
Manufactured by rotational molding. Plastisol (PVC + plasticizer + blowing agent)
is poured into a heated sphere where it coats the wall of the rotated sphere and
then is heated to the point that the chemical blowing agent generates CO2
Problems we have seen with balls:
1) Wall thickness variation
2) Debris embedded in the ball wall (during
manufacture)
3) Outside surface has most cells ruptured
during manufacture
4) Material flaw sensitivity

6. Burst Test Results of Four
Different Colored Balls
2 of 2 blue and 2 of 2 green exploded
2 of 2 gold and 2 of 2 brown did not
Why???

7. Flaw Sensitivity Testing

8. Only Material Difference
Noted was Trace Metals

9. Conclusions
• Exercise balls should be manufactured and tested to ensure
they are highly burst resistant and free from defects.
• Most exercise balls are manufactured in China and we have
found significant problems with material contamination and
wall thickness variation (e.g., >300% variation!)
• Key to burst resistance and safety is making the balls from a
material that is not sensitive to flaws.
• I believe that it is time for ASTM / ISO to develop stringent
manufacturing/testing standards for exercise balls.