At what distance is noise measured in dB for shipping refrigerated containers?
Noise from shipping containers is measured at various distances depending on the purpose of measurement, type of equipment, and methodology used. Three main scenarios are essential:
- In ports and container terminals: For measuring equipment noise (e.g., cooling units, cranes), the standard distance is 1 meter (for refrigerated containers) or 15 meters (50 feet) (for heavy machinery according to American regulations).
- Impact on surrounding community: Noise is measured at the boundary of the property of the nearest “noise-sensitive receptor” (e.g., residential building, school) – the distance is variable, from tens of meters to kilometers depending on urban context.
- Underwater noise from ships: Scientific studies use a standardized theoretical distance of 1 meterfrom the source (ship propeller) – actual measurement occurs at various distances and is recalculated to this value.
Detailed Explanation
Types of noise and their sources in container logistics
Shipping containers are a complex system where various noise sources occur:
- Refrigerated (reefer) containers: Compressors, fans, possibly diesel engines of cooling units.
- Handling equipment: Portal and mobile cranes, forklifts, cargo tractors.
- Transport: Trucks, railway wagons.
- Ships: Engines, generators, propellers (including underwater noise).
Typical noise levels:
| Source | Noise level (dB) at 1 m |
|---|---|
| Whisper | 30 |
| Normal conversation | 50–65 |
| Refrigerated container | 62–72 |
| Road traffic | 70–85 |
| Industrial compressor | 70–90 |
| Diesel engine (nearby) | 80–100 |
Legislation and standards for noise measurement
Basic standards
- EN ISO 3744:2010 – Acoustics – Determination of sound power levels and sound energy of noise sources using sound pressure – Engineering methods for practically free field over a reflecting plane.
- ČSN ISO 10302-1 – Measurement of noise from small equipment.
- IEC 61672-1 – Specification of sound level meters.
Key points of EN ISO 3744:2010 standard
- Precise measurement methodology for industrial machinery (including container cooling units).
- Definition of measurement surface – hemispherical, rectangular, cylindrical, depending on equipment shape.
- Measurement from multiple points on the surface at precisely defined distance (typically 1 meter).
- Requirements for test environment – as close as possible to free field over a reflecting surface (e.g., concrete floor), outdoors or in a semi-anechoic chamber.
- Corrections – measurement must be at least 6 dB higher than ambient noise level, possible corrections for interference, etc.
- Calibration – mandatory use of calibrated measuring instruments.
Legislation in the Czech Republic and EU
- Operating noise limits are set by Act No. 258/2000 Coll. (on public health protection) and Government Regulation No. 272/2011 Coll.
- For residential zones, hygiene limits are set, e.g., 50 dB during the day, 40 dB at night (measured on the facade of a protected space).
- Specific requirements for ports and industrial areas are set by local territorial decisions and EIA assessments.
Practical noise measurement for shipping containers
Refrigerated containers (reefers)
- Noise levels: 62–72 dB(A) when measured at a distance of 1 m from the cooling unit.
- Main sources: Compressor vibrations, fans, diesel engines.
- Most commonly used standards: EN ISO 3744:2010, ČSN ISO 10302-1.
- Measurement is performed in accordance with the standard: microphones placed on a defined measurement surface (hemisphere 1 m above a reflecting plane), during normal equipment operation.
- Example manufacturers: Carrier Transicold, Thermo King, Daikin, Starcool.
- Noise reduction: Modern containers have anti-vibration mounting, quiet fans, soundproof enclosures, active monitoring.
Handling equipment and transport
- Cranes, tractors, forklifts: Measurement is often performed at a distance of 15 m (50 feet) according to foreign regulations (e.g., Los Angeles Municipal Code).
- Long-term average: For community noise, measurement is taken at the property boundary where a noise-sensitive receptor is located (e.g., residential building).
- Metrics: Most commonly “equivalent noise level” (Leq), CNEL (Community Noise Equivalent Level), or Lden (day-evening-night).
Underwater noise from ships
- Standard methodology: Actual measurement with hydrophone at distances of hundreds of meters to kilometers, recalculation to “source level” at a distance of 1 m from the propeller.
- Typical values: Large ships can reach 180–190 dB re 1 µPa @ 1 m in the low-frequency band 20–500 Hz.
- Impact: Affects marine mammals, fish, ecosystems; monitoring occurs within international projects (e.g., CTBTO, SOSUS).
Measuring impact on community
- Measurement at property boundary: Typically, noise level is measured on the facade of the nearest residential building or in a protected outdoor space.
- Long-term monitoring: Stationary measuring stations are used to monitor daily/night averages, peaks, and average values (Leq, Lmax, LAeq,T).
- Penalties for evening and night noise: In some EU countries and the USA, CNEL/Lden is used (increase of 5 dB in the evening, 10 dB at night).
Noise reduction: technical and legislative measures
Technical measures
- Anti-vibration mounting of compressors and cooling units.
- Quiet fans and air flow optimization.
- Soundproof enclosures and acoustic covers.
- Electric drives instead of diesel units in urban areas.
- Active monitoring and automatic shutdown of units outside operating hours.
Legal and territorial measures
- Establishment of operating hours when operation of noisy equipment is permitted.
- Protection zones and planting of vegetation between the terminal and residential buildings.
- Urban planning – minimum distances between terminals and residential buildings.
Key terms and definitions
| Term | Meaning |
|---|---|
| Sound level (dB, dB(A)) | Logarithmic measure of sound intensity, A-weighted scale reflects human ear sensitivity. |
| Refrigerated container (reefer) | Container with active cooling unit, used for transporting temperature-sensitive goods. |
| Acoustic power (Lw) | Total amount of acoustic energy radiated by a source per unit time. |
| Noise-sensitive receptor | Residential building, school, hospital, park – a place where increased protection from noise is required. |
| Ambient noise | Total sound level in a given space, including natural and anthropogenic sources. |
| Underwater noise | Sound propagated in water, typically generated by maritime transport – mainly ship propellers. |
| EN ISO 3744:2010 standard | International standard for measuring acoustic power of industrial equipment. |
Case study: noise measurement in practice
Los Angeles and Long Beach ports (USA):
- Within studies “Noise Screening Analysis for Berths 97-109,” main noise sources were identified: trucks, cranes, trains, and ships in docks.
- A 3D model of the port was created that simulates noise propagation from individual sources to the surroundings.
- Equipment noise was measured at a distance of 15 meters (50 feet), community noise at the boundary of residential areas.
- Results were used to adjust operations, invest in quieter equipment, and establish protective measures.
Refrigerated containers in urban areas (Czech Republic, EU):
- Typical values 62–72 dB(A) at a distance of 1 m from the unit.
- In residential zones, requirement to implement quieter models, restrict night operation, and emphasize regular maintenance.
Latest trends and innovations
- Development of “quiet” cooling units: Noise reduction below 60 dB(A) through new fan designs, anti-vibration elements, electronic control.
- Hybrid and electric drives: Urban ports are adopting electric units instead of diesel, significantly reducing emissions and noise.
- Automated monitoring systems: Online measurement and data recording enables immediate intervention when limits are exceeded.
- Green barriers and urban solutions: Tree planting, noise barriers, optimization of terminal internal layout.
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