To ensure Class 4 and Class 3B laser beams do not escape from laser laboratory or medical facilities, including hospital theatres, certified laser blocking material should be installed. Ordinary curtains are rarely capable of stopping a laser beam and specially designed certified laser blocking material must be used (certified to IEC/EN 60825-4).
Also, production facilities using Class 1 lasers, which are Class 4 under service conditions, may require ceiling-mounted curtains to allow other work to continue safely in the same room during service…
Invinity to build 20MWh flow battery in UK
A surprising comment for someone who (I think you´ve said in the past) worked in the industry. National Grid have a variety of reserve service schemes...