Subpart C
The purpose is to set test and performance requirements for protective frames (ROPS) so they reduce the frequency and severity of operator injuries from accidental tractor upsets. See the purpose in 1928.52(a) and the general operator protection requirement in 1928.51.
A protective frame model must be tested by (1) a laboratory energy‑absorption test (static or dynamic) and (2) a field‑upset test to the side and rear under controlled conditions, unless an exception applies. See 1928.52(b) and the detailed subparagraphs at 1928.52(b)(1) and 1928.52(b)(2).
The field‑upset test can be omitted when laboratory test analysis shows the frame's energy absorption ratios exceed the standard margins: either (A) both FERis and FERir exceed 1.15 from the static energy‑absorption analysis, or (B) the dynamic test shows the frame can withstand an impact 15% greater than the required impact for the tractor weight. See 1928.52(b)(2)(i) and 1928.52(b)(2)(ii), and the FER definitions in 1928.52(d)(2)(ii).
A protective frame is a structure of uprights mounted to the tractor and extending above the operator's seat designed to protect the operator in an upset. A typical two‑post frame example is shown in the standard. See the definition at 1928.52(c)(1).
Yes — an overhead weather shield or an overhead falling‑object protection device may remain attached during tests provided it does not contribute to the strength of the protective frame. See 1928.52(c)(2) and 1928.52(c)(3).
Use the weight of the heaviest tractor model on which the protective frame is to be used; each test must be performed on a new protective frame with the same mounting‑connection design; and instantaneous deflection must be measured and recorded for each segment of the test. See 1928.52(d)(1)(i), 1928.52(d)(1)(ii), and 1928.52(d)(1)(iii).
No — rear input energy tests (static, dynamic, or field‑upset) are not required for frames mounted on tractors that have four driven wheels and place more than one‑half of their unballasted weight on the front wheels. See 1928.52(d)(1)(vii).
For static tests the laboratory mounting base must be the tractor chassis or its equivalent; the frame must be instrumented to obtain required load‑deflection data at specified locations; and for one‑ or two‑upright designs, mounting connections must be instrumented to record forces before any installation load is applied. See 1928.52(d)(2)(i)(A), 1928.52(d)(2)(i)(B), and 1928.52(d)(2)(i)(C).
The side input energy Eis = 723 + 0.4 W (ft‑lb) and the rear input energy Eir = 0.47 W (ft‑lb), where W is tractor weight in pounds; FER (factor of energy ratio) is the ratio of strain energy absorbed Eu to required input energy (FERis = Eu/Eis and FERir = Eu/Eir). See the definitions and formulas at 1928.52(d)(2)(ii).
The rear static load is applied to the upper extremity of the frame at a point midway between the center of the frame and the inside of the frame upright, distributed on an area no greater than 160 sq. in. The rear test is stopped when the frame has absorbed the required Eir energy, when deflection exceeds the allowable deflection, or when the frame load limit is reached before allowable deflection. See 1928.52(d)(2)(iii)(A) and the stop criteria at 1928.52(d)(2)(iii)(A)(1)–(3).
Apply the side load to the upper extremity at a 90° angle to the vehicle centerline on the side farthest from the rear load, stop the test when the frame absorbs Eis or allowable deflection is exceeded or load limit is reached, then construct the L‑D curve and calculate Eis, FERis, and FSB as required. See 1928.52(d)(2)(iii)(F) and the follow‑up tasks at 1928.52(d)(2)(iii)(G)–(J).
Dynamic tests use a 4,410‑lb (2,000‑kg) pendulum with a 27±1 in. impact face, suspended from a pivot 18–22 ft above impact, with the tractor restrained by cables having strength at least that of 0.50‑in. steel cable (and limited elasticity), and tires inflated to manufacturer’s maximum operating pressure with no liquid ballast. See 1928.52(d)(3)(i)(B) and the restraining/tire requirements at 1928.52(d)(3)(i)(C) and 1928.52(d)(3)(i)(D).
Evaluate the frame first with a rear dynamic impact and then with a side impact on the same frame, using the pendulum height per paragraph (d)(3)(ii), positioning the pendulum so the initial impact point lies on the pendulum CG arc; for rear impact position the pendulum 20° from vertical before impact. See 1928.52(d)(3)(iii)(A) and 1928.52(d)(3)(iii)(B).
Restraining members must have strength no less than, and elasticity no greater than, that of 0.50‑in. (12.7‑mm) steel cable; attachment points must provide restraining cable angles of 15° to 30° to the horizontal and be located behind the rear axle and in front of the front axle as specified. See 1928.52(d)(3)(i)(C).
No repairs or adjustments may be made during the dynamic test; if any cables, props, or blocking shift or break during the test the test must be repeated. See 1928.52(d)(3)(i)(F) and 1928.52(d)(3)(i)(G).
The field‑upset side test must be conducted on a dry, firm soil bank with an average cone index of at least 150 (0–6 in. layer), and cone index must be determined per ASAE recommendation R313.1‑1971. See 1928.52(d)(4)(i)(B)(1) and the referenced ASAE standard citation at 1928.52(d)(4)(i)(B)(2).
Rear upsets must be induced by engine power driving the tractor forward up a minimum 60°±5° slope at 3–5 mph at governed rpm (or equivalent), and side upsets must be induced by driving under power at a minimum 10 mph (or max speed if under 10 mph) over the specified ramp. See 1928.52(d)(4)(ii)(A) and 1928.52(d)(4)(ii)(B).
Frames and nearby parts may deform but must not shatter, leave sharp edges, or encroach on the specified operator‑area clearances: d = 2 in. inside upright to vertical seat centerline, e = 30 in. longitudinal centerline, f = ≤4 in. rear edge of crossbar forward of the SRP, g = 24 in. minimum, and m ≤12 in. See 1928.52(e)(1)(i).
The SRP is the intersection where a vertical line tangent to the most forward point at the longitudinal seat centerline of the seat back meets a horizontal line tangent to the highest point of the seat cushion, determined with the seat unloaded and adjusted to its highest and most rearward position for seated operation. See 1928.52(d)(1)(iv).
The protective structure and fasteners must pass static, dynamic, or field tests at 0°F (−18°C) or the material must meet Charpy V‑notch impact‑strength minimums: for 10×10 mm specimen 8.0 ft‑lb at −20°F, 10×7.5 mm 7.0 ft‑lb, 10×5 mm 5.5 ft‑lb, or 10×2.5 mm 4.0 ft‑lb (all at −20°F). Specimens are longitudinal from flat, tubular, or structural stock before forming or welding. See 1928.52(e)(1)(ii).
For static tests both FERis and FERir must be greater than 1.0, and when the ROPS has only one or two uprights the mounting‑connection design margin FSB must be greater than 1.3. See 1928.52(e)(2).
Dynamic test performance must meet the structural requirements using the clearances and dimensions specified in paragraph (e)(1) for both side and rear impacts so that operator space is preserved during dynamic loading. See 1928.52(e)(3) and 1928.52(e)(1).
Instrumentation must be placed on mounting connections before any installation load is applied so that the required peak forces in the connections are recorded during testing. See 1928.52(d)(2)(i)(C).
OSHA will accept ROPS meeting the performance requirements of ISO test standards as equivalent when the SAE standard recognizes those ISO tests and the ROPS also meet the SAE/ASAE temperature/material and seat‑belt requirements; however OSHA does not independently verify equivalency — the employer is responsible for compliance. This is discussed in the OSHA letter on ROPS equivalency, which explains OSHA's willingness to accept ISO per SAE and ASAE [see the Letter of Interpretation at https://www.osha.gov/laws-regs/standardinterpretations/1997-07-08-0] and the regulatory ROPS requirements in 1928.51 and 1928.52.