Rain

On Friday, 25 August, when Harvey made landfall, the National Hurricane Center forecast announced 15–30 inches (380–760 mm) of rainfall, with isolated amounts up to 40 inches (1,000 mm). On Sunday, 27 August, the National Hurricane Center updated its forecast, indicating additional rainfall of 15–25 inches (380–640 mm) and up to 50 inches (1,300 mm) over the next several days.

When the flooding started, Arkema moved the temperature-sensitive chemicals into refrigerated trucks. Unfortunately, it was already too late to evacuate the trucks. The company decided to leave the trucks in place with two backup power systems. It was considered that if the trucks were stuck on a flooded and crowded highway, the consequences could have been serious.

Evacuation of the site and of the neighboring population living within 1.5 miles from the Arkema plant, hampered the rescue operations in the area.
A police officer was hospitalized after inhaling noxious fumes from the fire.

The water level was so high that the plant responders could do nothing to prevent the degradation and explosion of the chemical.
It was chosen to let the fire burn itself out, rather than put responders lives into danger. An evacuation of the site and of the neighboring population living within 1.5 miles from the Arkema plant in Crosby was called.
Only on Sunday, the company decided to ignite the remaining combustible containers rather than wait for them to explode on their own.

18

300

At least 18 (mostly responders) were injured by inhaling noxious fumes produced by the decomposing peroxides.

The plant was evacuated, with only a few plant personnel and emergency responders left.
An evacuation order was issued in a 1.5 mile radius circle around the facilities and was lifted only a few days later. People complained because they could not go back to their homes for several days.

The redundancy of the backup power system is pointless if they are all caught in the same natural event.
Since the facility is located in a known flood prone area, the safety-relevant equipment should be located on higher ground in order to survive flood events.

In at least one of Arkema's hazard mitigation plans filed with the federal government, plant officials acknowledged that flooding is a risk. The site sits in a FEMA "high-risk" floodplain that has flooded in the past, leading to a power failure. That time, the site only had six inches of water. In that 2006 incident, strikingly similar to the 2017 incident, the plant flooded, lost power and materials ignited inside a warehouse. There is no indication that the company made any changes in its backup systems in response (e.g. moving backup power generators to higher ground).