13 ENVIRONMENT. HEALTH PROTECTION. SAFETY 13.030 Wastes 13.030.20 Liquid wastes. Sludge 13.060 Water quality 13.060.30 Sewage water 23 FLUID SYSTEMS AND COMPONENTS FOR GENERAL USE 23.040 Pipeline components and pipelines 23.040.50 Pipes and fittings of other materials 29 ELECTRICAL ENGINEERING 29.120 Electrical accessories 29.120.10 Conduits for electrical purposes 33 TELECOMMUNICATIONS. AUDIO AND VIDEO ENGINEERING 33.040 Telecommunication systems 33.040.99 Other equipment for telecommunication systems 45 RAILWAY ENGINEERING 45.040 Materials and components for railway engineering91 CONSTRUCTION MATERIALS AND BUILDING 91.080 Structures of buildings 91.080.40 Concrete structures 91.100 Construction materials 91.100.30 Concrete and concrete products 91.100.40 Products in fibre-reinforced cement 93 CIVIL ENGINEERING 93.010 Civil engineering in general 93.025 External water conveyance systems 93.030 External sewage systems 93.080 Road engineering 93.080.20 Road construction materials 93.120 Construction of airports 93.140 Construction of waterways, ports and dykes |