If the utility is forced to increase rates sharply, the costs may take an economic toll. Manufacturing companies could choose to move their businesses out of the service area or even the state. Residential customers within the utility’s territory then could be left to cover the costs.

“This becomes a humongous challenge,” Mr. Cooper said. “If they try and raise the prices, they may not be able to get them. Should they even be allowed to recover all the cost, if they were guilty of imprudent behavior?”

PG&E said its liability insurance for the year that began Aug. 1 amounted to $1.4 billion.

Lynsey Paulo, a spokeswoman for PG&E, said the utility was focused on helping fight the current wildfires rather than the company’s economics. The company has set up a base camp with 800 employees in the area of the Camp Fire, she said, a figure that is expected to grow to 1,000 by the end of the week and could reach 3,000.

“We’re not going to speculate on what may or may not be impacting the stock market,” Ms. Paulo said.

Critics of the utilities say poor maintenance of power poles and failure to trim vegetation around power lines is a major cause of fires. On a walking tour last spring in San Jose, a former state regulator showed overloaded poles bending under the weight of wires and cables, as well as power lines running through tree foliage.

PG&E’s “safety culture” has been the subject of a three-year investigation by the state’s Public Utilities Commission. The agency is expected to act on the inquiry’s findings as early as this month.