Q. For onboard noise measurement as per IMO code of Noise Level onboard Ships, Explain the requirements regarding:-
A. Measuring conditions
B. Measuring equipment
C. Measurement procedures
Answer:-
A. MEASURING CONDITIONS
Operating conditions at sea trials
a. Measurements should be taken with the ship in the loaded or ballast condition
b. Noise measurements shall be measured at the normal service speed &, unless otherwise addressed in the provisions below, no less than 80% of the MCR.
c. All machinery, navigation instruments, radio & radar sets, etc., generally in use at normal seagoing condition & levels. However, neither energized fog signals nor the helicopter operations shall take place during taking of these readings.
d. Measurements in the spaces containing emergency diesel engine driven generators, fire pumps or other emergency equipment that would generally be run only in an emergency, or for test purposes, shall be measured with the equipment operating
e. Mechanical ventilation, heating & air-conditioning equipment shall be in normal operation, considering that the capacity shall be in compliance with the design conditions.
f. Doors & windows should in general be closed
g. Ships fitted with the bow thrusters, stabilizers, etc., may be subject to high noise levels when this machinery is in operation. For the thrusters, measurements shall be made at 40% thruster power & the ship’s speed shall be suitable for the thruster operation
Operating conditions at the port
a. When the noise level from the ship’s cargo handling equipment may leads to the noise above maximum levels in the duty stations & accommodation spaces affected by its operation, reading should be taken
b. Where the ship is a vehicle carrier and noise during loading and discharging originates from vehicles, the noise level in the cargo spaces and the duration of the exposure should be considered in conjunction
B. MEASURING PROCEDURES
a. During noise level measurement, only seafarers required for the operation of the ship & persons taking the reading shall be present in the space concerned
b. Sound pressure level readings shall be taken in the decibels using an A-weighting (dB(A)) & C-weighting (dB(C)) filter & if required also in octave bands between 31.5 & 8,000 Hz.
c. The noise level readings shall be taken with the integrating sound level meter using spatial averaging & over a time period until stable readings are found or at least 15 seconds in order to show the average value from variations due to irregular operation or variations in the sound field. Measurements shall be made only to the nearest decibel.
d. If the first decimal of the dB reading is 5 or higher, the reading shall be made to nearest higher integer.
e. Readings shall be taken with the microphone at a height of between 1.2 m (seated person) & 1.6 m (standing person) from deck.
f. The distance between the two measurement points should be at least 2 m, & in large spaces not containing machinery, readings should be taken at intervals not greater than 10 m throughout the space including positions of the maximum noise level. In no case shall readings be taken closer than 0.5 m from the boundaries of a space
g. Reading shall be taken at the principal working & control stations of the seafarers in the machinery spaces & in the adjacent control rooms, if any, special attention being paid to telephone locations & to positions where voice communication & audible signals are important
h. Readings should not generally be taken closer than 1 m from operating machinery, or from decks, bulkheads or other large surfaces, or from the air inlets. Where this is not possible, measurement shall be taken at a position midway between the machinery & adjacent reflecting surface.
i. Readings shall be taken on both navigating bridge wings but should only be taken when the navigating bridge wing to be measured is on the lee side of the ship
j. The number of the measurement cabins shall be not less than 40 per cent of total number of the cabins. Cabins which are obviously affected by the noise, i.e. cabins adjacent to machinery or casings, must be considered in any case.
C. MEASURING EQUIPMENT
a. Equipment Specification
- Sound Level Meters:- Measurement should be done using precision grade sound meters, industrial grade sound meters, integrating sound meter
- Octave Filter set:- Used alone or in conjunction with the sound level meters
- Measurement Microphones:- Should be of random incidence type
b. Selection of Equipment
- It is advised that where the noise level is closer to limits; precision type to be used
- When measuring the fluctuating type noise; integrated sound level meter to be used
- Sound level meter & calibrator should be calibrated by shore at interval not more than 2 years
- A microphone windscreen to be used when taking readings of noise outside
- Measuring equipments should not use flammable gas/air mixture areas, unless equipment certified intrinsically safe
