American Society of Mechanical Engineers, Inc. v Hydrolevel Corp. (1982) may be the case you are referring to. From here:
Hydrolevel developed a mechanism that included a time delay in its fuel cutoff system, claiming that this would ensure a more reliable determination of water level in boilers whose water is in motion. ASME's BPVC Boiler and Pressure Vessel Committee was headed by prominent representatives of two companies then dominating the market. Unknown to Hydrolevel, a letter was circulated that insisted that low-water fuel cutoff mechanisms should operate immediately. By the time Hydrolevel discovered the existence of this letter, it had suffered serious market losses.
It seems that one company (McDonnell and Miller) requested clarification from the committee on a standard, and received a reply from the volunteer chairman of the committee who was also an employee of another company (Hartford Steam Boiler Inspection and Insurance Company) and then used that clarification as a way to boost their sales at the expense of Hydrolevel.
Some more background from here:
T.R. Hardin, chairman of the ASME committee and employee of the Hartford Steam Boiler Inspection and Insurance Company in Connecticut, wrote the original response to McDonnell and Miller's inquiry. ASME's interpretation was used by McDonnell and Miller salesmen as proof of Hydrolevel's noncompliance. Subsequently, Hydrolevel never acquired sufficient market penetration for sustaining business, and eventually went bankrupt.
Hydrolevel sued McDonnell and Miller, the Hartford Steam Boiler Inspection and Insurance Company and ASME arguing that two ASME subcommittee members acted not only in the self-interest of their companies, but also in violation of the Sherman Anti-Trust Act.
It doesn't quite fit your memory, as it doesn't seem to have been brought about because of any loss of life (at least from what I have read about it so far), and I also didn't see any qualitative determination on whether the interpretation of the standard by ASME was any better or worse than Hydrolevel's implementation, but it does 1) Concern steam boilers, and 2) Involve a conflict of interest on a standards body.
Also, I should also note that the only one found liable was ASME. The two companies settled with Hydrolevel out of court. ASME was found liable for $4.75 million in damages, though after the Hydrolevel CEO died of a heart attack after being informed of a Jury's verdict in his favor in lower court.