All areas where hydrogen is stored or used should contain a permanent placard stating:
WARNING: HYDROGEN - FLAMMABLE GAS - NO SMOKING - NO OPEN FLAMES
Storage sites for liquefied hydrogen should also have a sign that reads:
WARNING: LIQUEFIED HYDROGEN - FLAMMABLE GAS - NO SMOKING - NO OPEN FLAMES
Signs should be placed on all liquid hydrogen vessels near the pressure-relief valve vent stack stating:
WARNING: DO NOT SPRAY WATER ON OR IN THE VENT OPENING.