Based on recent updates from USCG and NFPA, we now know that two days after the incident, a marine chemist arrived on the scene in Alaska and tested the atmosphere of the barge involved in the accident. But the atmosphere therein had been sufficiently ventilated to allow firefighters to enter and recover the body of the worker. So, in an effort to determine the condition of the atmosphere of the port-side barge before the workers entered, Coast Guard personnel and the marine chemist tested the atmosphere of the not-yet-opened starboard-side barge.
The oxygen content was 0.7% by volume; the combustible gas indicator read 24% of the lower explosive limit (LEL), and the concentration of carbon monoxide was 12 ppm.
Most combustible gas sensors depend on oxygen to function properly. Most sensor manufacturers state that if the oxygen concentration in the sampled atmosphere is 11% by volume or less, the sensor cannot provide an accurate reading. Because the oxygen content was less than 1% by volume in the barge, the chemist retested the atmosphere with an infra-red (IR) combustible gas indicator. The IR combustible gas indicator (IR-CGI) does not depend on oxygen to produce a test result. The combustible gas reading with the IR-CGI was 0% LEL.
The marine chemist observed corroded steel, mud, and slime inside the barge. The confined spaces on this barge had reportedly not been opened for many years, allowing the oxidation and decomposition processes to continue without abatement.
See the NFPA article on this event