Two workers were assigned to replace a water valve located in an underground concrete vault. After removing the manhole cover, worker #1 climbed down the ladder into the vault. Worker #1 collapsed and became unconscious within seconds of reaching the bottom. Worker #2 went down the ladder to rescue worker #1 but was quickly overcome by the lack of oxygen. Both workers died at the bottom of the vault. Answer must be at least 200 words in length and all references cited in APA format. 

Discuss how you could apply the Haddon matrix theory to investigate this accident. You may make additional assumptions about the scenario, as needed, for your discussion.