Specifications Part 1 - Water Supply, Sewerage and Tube Well Works

14.6.3 The most serious hazards of manhole work are however flammable gas andoxygen deficiency. The workers should be thoroughly trained to carry outsimple tests on every manhole before entry to detect oxygen deficiency,combustibles, carbon monoxide or hydrogen sulphide.14.6.4 Ventilate the sewer line by opening two or three manholes on both the sideswhere work is to be carried out. This is more important when adequate blowersfor ventilating sewers are not available. The manholes should be opened atleast one hour before start of operations. The opened manholes should beproperly fenced to prevent any person, especially children, accidentally fallinginto the sewer. Dummy covers with BRC welded fabric can be used.14.6.5 Where it is desirable to use the blowers, operate these for at least 30 minutesbefore start and during cleaning operations to ventilate the lowest workinglevels.14.6.6 Use safety harness and life line before entering the sewer line. Two helpers atthe top should be provided for each person. The person standing at the topmust send signals at every few minutes interval to the person in the manhole toensure safety.14.6.7 Test manhole rungs or steps for structural safety before using.14.6.8 Ensure that, where portable ladders are used, they are properly seated orfixed.14.6.9 Ensure that no material or tools are located near the edge which can fall intothe manhole and injure the workman.14.6.10 Lower all tools to the workman in a bucket.14.6.11 Use lighting equipment which must be explosion and fire proof.14.6.12 Use Gas masks when men have to enter into the sewer line.14.7 Covers and frames: -14.7.1 The size of manhole covers should be such that there should be clear openingof not less than 560mm diameter for manholes exceeding 0.9m depths.14.7.2 When cast iron manhole covers and frames are used they shall confirm to IS1726 (parts 1 to 7). The frames of manhole shall be firmly embedded to correctalignment and level in plain concrete on the top of masonry. After completion ofthe work, manhole covers shall be sealed by means of thick grease.14.7.3 Where sewer are to be laid in high subsoil water conditions, manholes maybeconstructed in R.C.C. of grade M20 or 1:1.5:3. The manholes in this type ofconstruction preferably shall be circular.Urban Administration & Development Department Page 165