Specification for visors for non-metal police and firemen's helmets
1981 Edition

This section defines the extent and application of the standard, including specifications and testing methods for optical devices such as telescopes, materials like phenolic and polyethylene molding compounds, firemen’s helmets, and acrylic sheets used in lighting. Key telescope parameters include magnification ranging from 7.5 to 20 (with 15 recommended), aperture size between 15 to 20 mm, and adjustable eye-pieces with graticules. Calibration procedures involve aligning the telescope coaxially with the target optical system at a distance of 4.6 ± 0.1 meters using a parallel beam of light, with fine focus adjustments to measure power changes as small as 0.01 m⁻¹.

Defines critical terms such as the visor screen—a curved transparent polycarbonate sheet designed for eye and face protection—and telescope specifications including magnification, aperture, adjustable eye-piece, and quality checks for image distortion. It also outlines the polycarbonate sheet criteria, emphasizing physical properties like transparency and impact resistance, and notes on numerical rounding per the standard.

Details the physical requirements for the polycarbonate sheets used in visors, including a minimum relative density of 1.2 and tensile strength not less than 600 kgf/cm² as per IS 2530-1963. The visor thickness is specified as 3.0 ± 0.2 mm. Material must be optically clear and comply with the physical properties listed in Appendix A, ensuring durability and clarity.

Specifies the construction parameters including minimum relative density of 1.2, light transmission of at least 80%, and use of optically clear transparent polycarbonate of 3.0 ± 0.2 mm thickness. The visor must meet mechanical and optical standards detailed in Appendix A to guarantee impact resistance, durability, and optical clarity.

Describes requirements for visor assembly, including secure bolting to helmet shells, absence of defects such as cracks or burrs, and smooth, uniform surfaces free from discoloration. Material must be self-extinguishing in flame per IS 2745:1969 and maintain a minimum light transmission of 80%. These criteria ensure durability, safety, and user comfort.

Sets a maximum mass of 350 grams for the complete visor assembly. If the weight exceeds this limit, the precise mass (rounded to the nearest 10 grams) must be clearly labeled. Material properties such as relative density (≥ 1.2) and tensile strength inform weight calculations, ensuring the visor remains lightweight for operational comfort.

Outlines key instructions including adherence to the 350-gram maximum mass limit with mandatory labeling for heavier visors, use of curved transparent polycarbonate material for adequate protection, and application of revised numerical rounding procedures. Emphasizes the importance of lightweight design and clear marking for user awareness.

Details marking requirements such as imprinting the manufacturer's name or trademark and year of manufacture on the visor. Optional inclusion of the ISI certification mark is permitted. The visor must have fixing holes with a diameter of at least 6 mm and a curvature radius matching the helmet shell. Target plates and optical test patterns are specified for quality assurance.

Lists the physical characteristics required for polycarbonate visor sheets, including thickness of 3.0 ± 0.2 mm, optical clarity, and transparency. Fixing holes must be at least 6 mm in diameter to facilitate secure attachment. Marking with manufacturer’s details and production year is mandatory to ensure traceability.

Describes methods for assessing visor optical quality, including telescope specifications, calibration setup involving alignment with a target illuminated by a parallel light beam at 4.6 ± 0.1 meters, and precise measurement of refractive power changes. Procedures also cover astigmatism measurement and standard lens tolerances to verify minimal distortion.

Specifies the method for measuring light transmission and haze through the visor material using spectrophotometric techniques as per IS 7569-1975 Appendix G. Minimum light transmission is set at 80%, with diffuse transmittance not exceeding 5%. Testing ensures optical clarity and compliance with safety standards.

Summarizes the flammability test requiring the material to be self-extinguishing according to IS 2745:1969 Appendix H. The test involves exposing a specimen to flame for a specified duration, then observing extinguishment time and absence of flaming drips. Compliance ensures the visor’s flame resistance and safety in operational environments.