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ASME B56.11.5-1992 (2000) — Measurement of Sound Emitted by Low Lift, High Lift, and Rough Terrain Powered Industrial Trucks
🔊 ASME B56.11.5-1992 (2000) is one of the ASME B56.11 standardization sub-series. It defines how to measure the sound emitted by low lift, high lift, and rough terrain powered industrial trucks — that is, electric and internal-combustion forklift trucks of all main types. By standardizing the acoustic environment, microphone positions, truck operating conditions, and data processing, the Standard makes noise data from different manufacturers and models comparable and repeatable. It provides a common basis for manufacturers to declare noise values, for users to evaluate occupational noise exposure on site (against OSHA noise limits), and for purchasers to compare equipment. It was published in 1992 and reaffirmed in 2000.
💡 Why declared noise matters: the same truck behaves very differently acoustically in a workshop, a warehouse, or outdoors. B56.11.5 yields a “comparable nominal value” measured in a defined acoustic environment and duty, so users can rely on the nominal data for acoustic planning and hearing-protection decisions instead of comparing brands by feel.
1. Measurement Method Framework 📌
The measurement method builds on the internationally accepted “engineering method”. Its core elements include:
- Test environment: preferably a semi-anechoic chamber or an open site; an alternative is a free field over a reflecting plane, with corrections for background noise and site absorption.
- Microphone positions: microphones placed around the vehicle at a defined height (typically 1.2 m or 1.5 m, related to the driver’s ear position) and defined distances (e.g., 7 m from the vehicle envelope or as given per truck type) at several measurement points.
- Operating conditions: the fully loaded truck passes the measurement zone in a straight line at its maximum travel speed; hydraulic lifting and idling may be measured as supplementary duty conditions.
- Data processing: A-weighting is applied, and the maximum sound pressure level or equivalent continuous level is recorded; several runs are averaged with the specified environment correction.
- Reporting: results are given as A-weighted sound power level (LWA) and/or sound pressure levels at the driver position and at the side, with a statement of test conditions.
⚠️ Distinguish the two measurement goals: B56.11.5 measures the vehicle’s emitted sound (for product declaration and comparison). Driver-ear noise exposure belongs to occupational health assessment and must be measured by the methods of OSHA 29 CFR 1910.95 or an equivalent occupational noise standard. The positions, duty, and purpose differ — never mix the data sets.
2. Measurement Positions and Duty Requirements 🔧
| Measurement Element | Typical Requirement | Remarks |
|---|---|---|
| Acoustic environment | Semi-anechoic / open site, environment correction if needed | Background noise must be sufficiently below the measured signal |
| Microphone height | e.g., 1.2–1.5 m (driver ear related) | Side points and driver position measured separately |
| Measurement distance | As given by truck size (e.g., 7 m outside the envelope) | Points distributed around all four sides |
| Vehicle condition | Full load, normal operating temperature | Tire pressure and gear selection per the manual |
| Duty conditions | Straight pass at maximum speed + lifting/idling supplements | Steady-speed passage through the zone |
| Weighting and values | A-weighted, maximum or equivalent continuous level | Averaged over several runs |
| Result expression | dB(A) sound pressure and/or sound power | State uncertainty and environment correction |
🚨 Never skip the environment correction: data measured in an ordinary workshop (strong reflections, high background noise) without correction can overstate the true value by several decibels. Decibels are nonlinear — any comparison is only valid on the same measurement basis and environment.
3. Engineering Practice Essentials 🛠️
- 🔍 Purchase comparison: compare declared B56.11.5 noise data across brands horizontally (same duty, same microphone-point definition) as part of the selection criteria.
- 📐 Acoustic planning: estimate area noise levels from fleet size, operating hours, and workshop acoustics; plan noise barriers, absorption, and hearing-protection zones.
- 🧪 Hearing protection: combine time-weighted average (TWA) exposure for drivers and bystanders; at the OSHA action level (85 dB(A) TWA), provide hearing protectors and audiometric testing.
- 📅 Condition monitoring: unusual noise often precedes faults in the hydraulic system, tires, drive train, or exhaust — include noise checks in routine maintenance.
- 📋 Declaration management: manufacturers should state the test conditions and method basis in technical literature; users should verify that declarations were obtained per B56.11.5.
4. Frequently Asked Questions ❓
❓ Q: How does B56.11.5 relate to occupational noise-exposure measurement (OSHA)?
A: B56.11.5 provides a standardized nominal value of vehicle-emitted sound for declaration and comparison. Exposure assessment must be done per OSHA 29 CFR 1910.95 by measuring the actual individual noise dose of drivers in the real work environment. The two are different purposes and are not interchangeable.
A: B56.11.5 provides a standardized nominal value of vehicle-emitted sound for declaration and comparison. Exposure assessment must be done per OSHA 29 CFR 1910.95 by measuring the actual individual noise dose of drivers in the real work environment. The two are different purposes and are not interchangeable.
❓ Q: Why measure in an “open site” — cannot I measure in the workshop?
A: Reflections and reverberation are added to the measured signal, making results higher and unstable. The Standard requires a correctable acoustic environment to obtain stable, comparable nominal values; on-site noise can only be estimated by simplified methods and cannot be used for declarations.
A: Reflections and reverberation are added to the measured signal, making results higher and unstable. The Standard requires a correctable acoustic environment to obtain stable, comparable nominal values; on-site noise can only be estimated by simplified methods and cannot be used for declarations.
❓ Q: Is the noise data a “maximum sound pressure level” or a “sound power level”?
A: Both are reported. Sound power level characterizes the total source strength of the vehicle and is environment-independent, best for comparing equipment; sound pressure level characterizes the field at a specific location, best for assessing the level at a point. B56.11.5 standardizes the measurement and reporting of both.
A: Both are reported. Sound power level characterizes the total source strength of the vehicle and is environment-independent, best for comparing equipment; sound pressure level characterizes the field at a specific location, best for assessing the level at a point. B56.11.5 standardizes the measurement and reporting of both.
🔍 Q: Electric trucks are much quieter than internal-combustion ones — is measurement still necessary?
A: Yes. Electric trucks still produce significant noise from the hydraulic pump, lift motor, and traction motor, and their high-frequency content should not be ignored for hearing; their overall level is of course usually much lower than IC trucks — which is exactly the conclusion a unified method quantifies.
A: Yes. Electric trucks still produce significant noise from the hydraulic pump, lift motor, and traction motor, and their high-frequency content should not be ignored for hearing; their overall level is of course usually much lower than IC trucks — which is exactly the conclusion a unified method quantifies.
