IS 939:1977 is the Indian Standard (BIS) for snatch block for use with fibre rope for fire brigade use. This standard lays down the specifications for materials, dimensions, workmanship, and testing of snatch blocks specifically designed for use with fibre ropes. It is primarily used by fire brigades for rescue and general lifting operations.
Specification for Snatch Block for Use with Fibre Rope for Fire Brigade Use
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Primary Strength Rating | Safe Working Load (SWL), e.g., 4.0 kN for 16 mm rope block | Minimum Breaking Strength (MBS), e.g., ≥36 kN for a 'General Use' pulley | NFPA 1983:2022 |
| Proof Load / Static Test | 2 x Safe Working Load (SWL) | 4 x Working Load Limit (WLL) without failure | EN 13157:2004+A1:2009 |
| Designated Rope Type | Manila (natural fibre) rope | Synthetic kernmantel life safety rope | NFPA 1983:2022 |
| Material Specification | Prescriptive (e.g., Gunmetal shell, Phosphor Bronze sheave) | Performance-based (e.g., high-strength aluminum alloys, stainless steel) | NFPA 1983:2022 |
| Hook/Connector Requirement | Trapezoidal hook without a latch | Hook must have a safety latch, or a closed connector like a carabiner is used | EN 13157:2004+A1:2009 |
| Minimum Sheave/Rope Diameter Ratio | 5:1 | Performance-based; no strict ratio, but must pass tests. Industry best practice for synthetic rope is often >8:1. | NFPA 1983:2022 |
| Marking Standard | Manufacturer, SWL, rope size | Manufacturer, MBS, rope diameter range, standard compliance (e.g., NFPA 1983 G), traceability code | NFPA 1983:2022 |