# CDC 4b051 Practice Test

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End Of Course Practice Test

• 1.

### (401) In ventilation work, what pressure is exerted outward against the interior surface of an enclosure?

• A.

Positive static

• B.

Negative static

• C.

Positive velocity

• D.

Negative velocity

A. Positive static
Explanation
In ventilation work, positive static pressure is exerted outward against the interior surface of an enclosure. This means that the pressure inside the enclosure is higher than the pressure outside, causing air to be pushed outwards. Positive static pressure is commonly used to ensure proper airflow and ventilation in buildings, preventing the buildup of contaminants and maintaining a comfortable environment.

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• 2.

### (401) After the fan of a ventilation systemis turned on, there is a conversion of

• A.

Total pressure of static pressure

• B.

Total pressure to velocity pressure

• C.

Velocity pressure to static pressure

• D.

Static pressure to velocity pressure

D. Static pressure to velocity pressure
Explanation
When the fan of a ventilation system is turned on, it causes the conversion of static pressure to velocity pressure. This means that the pressure exerted by the air in the system, which is initially static or still, is transformed into a pressure associated with the velocity or movement of the air. This conversion occurs as the fan forces the air to move, increasing its velocity and consequently its pressure. Therefore, the correct answer is "static pressure to velocity pressure."

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• 3.

### (401) The value for velocity pressure in a ventilation system is

• A.

Always positive

• B.

Always negative

• C.

Negative on the blowing side

• D.

Negative on the exhausting side

A. Always positive
Explanation
In a ventilation system, velocity pressure refers to the pressure exerted by the movement of air. Since pressure is a scalar quantity, it only has magnitude and no direction. Therefore, velocity pressure cannot be negative. It is always positive, regardless of whether it is on the blowing side or the exhausting side of the system.

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• 4.

### (402) Friction losses in a ventilation system can be reduced by increasing the

• A.

Hood size

• B.

Duct length

• C.

Duct velocity

• D.

Duct diameter

D. Duct diameter
Explanation
Increasing the duct diameter can help reduce friction losses in a ventilation system. Friction losses occur when air flows through the ducts and encounters resistance, causing a drop in pressure. By increasing the duct diameter, the cross-sectional area of the duct increases, allowing for smoother airflow and reducing the resistance to flow. This helps to minimize friction losses and maintain a higher pressure in the system, resulting in improved ventilation efficiency.

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• 5.

### (403)  A density factor of one means that the air you are dealing with is at

• A.

A high altitude

• B.

Standard conditions

• C.

Elevated temperature

• D.

High barometric pressure

B. Standard conditions
Explanation
A density factor of one means that the air you are dealing with is at standard conditions. Standard conditions refer to a set of predefined atmospheric conditions, including a temperature of 25 degrees Celsius (77 degrees Fahrenheit) and a pressure of 1 atmosphere (101.3 kilopascals or 14.7 pounds per square inch). These conditions are used as a reference point for various scientific calculations and measurements.

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• 6.

### (403) which type of velocity refers to the ability of a ventilation system to remove contaminants from a work area?

• A.

Face velocity

• B.

Duct velocity

• C.

Capture velocity

• D.

Transport velocity

C. Capture velocity
Explanation
Capture velocity refers to the type of velocity that refers to the ability of a ventilation system to remove contaminants from a work area. It is the velocity at which air must be moving in order to capture and remove contaminants before they can disperse into the surrounding area. By maintaining a higher capture velocity, the ventilation system can effectively control and remove contaminants, ensuring a safe and clean work environment.

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• 7.

### (404) What are two parameters at a given point in ventilation systems that are needed to calculate the air flow volume?

• A.

Area and pressure

• B.

Area and velocity

• C.

Velocity and pressure

• D.

Diameter and velocity

B. Area and velocity
Explanation
To calculate the air flow volume in ventilation systems, two parameters are required: area and velocity. The area refers to the cross-sectional area through which the air flows, while the velocity represents the speed at which the air is moving. By multiplying the area and velocity, the air flow volume can be determined.

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• 8.

### (404) Areas of ducts and hoods myst be expressed in

• A.

Inches

• B.

Linear feet

• C.

Square feet

• D.

Cubic feet per minute

C. Square feet
Explanation
The correct answer is square feet because when measuring the areas of ducts and hoods, we are interested in the two-dimensional space they occupy. Square feet is a unit commonly used to express the area of a flat surface. It represents the product of the length and width of a space in feet, providing a measurement of the total area in square units. This unit is appropriate for determining the size or capacity of ducts and hoods, as it gives an indication of the surface area they cover.

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• 9.

### (405)  Which is the maximum amount of a certain chemical vapor that air can hold at a given temperature?

• A.

Vapor pressure

• B.

Explosive limit

• C.

Saturation concentration

• D.

Required air flow volumes

C. Saturation concentration
Explanation
Saturation concentration refers to the maximum amount of a certain chemical vapor that air can hold at a given temperature. It represents the point at which the air is fully saturated with the vapor and can no longer hold any more of it. This is determined by factors such as temperature, pressure, and the specific properties of the vapor.

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• 10.

### (406) Other than good contaminant control, what is the biggest advantage of local exhaust over dilution ventilation?

• A.

Less noise

• B.

Lower operating costs

• C.

Better protection for equipment

• D.

B. Lower operating costs
Explanation
The biggest advantage of local exhaust over dilution ventilation is lower operating costs. Local exhaust systems are designed to remove contaminants at the source, resulting in a more efficient and targeted approach to ventilation. This means that less energy is required to circulate and treat the air in the entire space, leading to cost savings in terms of electricity consumption and maintenance. Dilution ventilation, on the other hand, involves mixing contaminated air with clean air to reduce the concentration of contaminants, which requires more energy and can be more expensive to operate.

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• 11.

### (407) Increasing the velocity of air through a slot hood without increasing the air flow volume most ofter results in

• A.

An increase in contaminant control

• B.

A decrease in contaminant control

• C.

An increase in system resistance

• D.

A decrease in system resiste

C. An increase in system resistance
Explanation
Increasing the velocity of air through a slot hood without increasing the air flow volume most often results in an increase in system resistance. This is because increasing the velocity of air through a slot hood creates more resistance for the air to flow through the system. As a result, the overall system resistance increases.

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• 12.

### (408) What may be indicated by a very strong flow coming in an open door of a room containing a local exhaust system?

• A.

• B.

Excessive crossdrafts

• C.

• D.

Proper discharge of airway wi

Explanation
A very strong flow coming in an open door of a room containing a local exhaust system may indicate inadequate makeup air. This means that the exhaust system is not receiving enough fresh air to effectively remove pollutants and maintain a balanced airflow. The strong flow coming in the open door suggests that the room is trying to compensate for the lack of makeup air by drawing in air from outside. This can lead to poor ventilation and potential issues with air quality in the room.

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• 13.

### (409) The range of acceptable values for the air flow volume on routine tests is within what persentage of the baseline?

• A.

25%

• B.

20%

• C.

15%

• D.

10%

D. 10%
Explanation
The correct answer is 10%. This means that the range of acceptable values for the air flow volume on routine tests should be within 10% of the baseline value. In other words, if the baseline air flow volume is X, then the acceptable range would be X +/- 10%. This allows for a small margin of error in the air flow volume measurements during routine tests.

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• 14.

### (410) At the beginning of a sound wave, the molecules near the source are drawn away from the surrounding air to form an area of lower atmospheric pressure.  This process is known as

• A.

Resonance

• B.

Compression

• C.

Rarefaction

• D.

Amplification

C. Rarefaction
Explanation
At the beginning of a sound wave, the molecules near the source are drawn away from the surrounding air, creating an area of lower atmospheric pressure. This process is known as rarefaction.

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• 15.

### (410) Which is a sound wave that can be characterized by a single frequency?

• A.

Pure Tone

• B.

White Noise

• C.

Complex sound

• D.

Reference sound

A. Pure Tone
Explanation
A pure tone is a sound wave that consists of a single frequency. Unlike complex sounds or white noise, which contain multiple frequencies, a pure tone is characterized by a single frequency. Therefore, a pure tone is the correct answer to the question.

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• 16.

### (411) What is the characteristic of sound that we measure and report when we quantify sound?

• A.

Wave

• B.

Intensity

• C.

Weighting

• D.

Power level

B. Intensity
Explanation
When we quantify sound, the characteristic that we measure and report is the intensity. Intensity refers to the amount of energy that is carried by the sound wave per unit of area. It is commonly measured in decibels (dB) and represents the loudness or strength of the sound. The intensity of a sound can vary depending on factors such as distance from the source, the size of the source, and the medium through which the sound travels.

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• 17.

### (412) What term would describe hearing loss due to an explosion?

• A.

Tinnitus

• B.

Acoustic Trauma

• C.

Threshold shift

• D.

Auditory Fatigue

B. Acoustic Trauma
Explanation
Acoustic trauma refers to hearing loss caused by exposure to a sudden, loud noise such as an explosion. This type of hearing loss can be permanent and is often accompanied by other symptoms such as tinnitus, which is a ringing or buzzing sound in the ears. Threshold shift refers to a temporary change in hearing sensitivity, and auditory fatigue refers to temporary hearing loss due to prolonged exposure to loud sounds. However, neither of these terms specifically describes hearing loss caused by an explosion.

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• 18.

### (413) Identifying equipment that produces hazardous moise at the operator's position is the purpose of what?

• A.

C/T calculation

• B.

Noise dosimetry

• C.

Sound level meter survey

• D.

Hearing conservation program

C. Sound level meter survey
Explanation
A sound level meter survey is conducted to identify equipment that produces hazardous noise at the operator's position. This survey involves measuring the sound levels in the workplace using a sound level meter. By identifying equipment that produces excessive noise, steps can be taken to control and reduce the noise levels to protect the operator's hearing. This survey is an important part of a comprehensive hearing conservation program.

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• 19.

### (414) Assuming that altitude is not a factor, within what range should a sound level meter read when a 114 dB calibrator is placed over the microphone?

• A.

113.9-114.1

• B.

113.5-114.5

• C.

113-115

• D.

Exactly 114

B. 113.5-114.5
Explanation
The correct answer is 113.5-114.5. This range is given because the sound level meter should read within half a decibel (0.5 dB) of the calibrator's sound level. Therefore, the range starts at 113.5 dB (114 dB - 0.5 dB) and ends at 114.5 dB (114 dB + 0.5 dB). This allows for a small margin of error in the meter's readings.

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• 20.

### (414) If the sound level readings during one measurement difer by more that 6 dB(A), record the result as

• A.

The maximum level

• B.

The minimun level

• C.

3 dB(A) less than the maximum level

• D.

3 dB(A) more than the minimum level

B. The minimun level
Explanation
If the sound level readings during one measurement differ by more than 6 dB(A), the result should be recorded as the minimum level. This means that the lowest sound level reading obtained during the measurement should be recorded as the result, regardless of the other readings.

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• 21.

### (415) What characteristic should a noise dosimeter have for measurements to be compared to Air Force standards?

• A.

Threshold of 85 dB(A)

• B.

Exchange rate of 3 dB

• C.

Criterion level of 90 dB(A)

• D.

Upper detection limit of a least 110 dB(A)

B. Exchange rate of 3 dB
Explanation
A noise dosimeter should have an exchange rate of 3 dB for measurements to be compared to Air Force standards. The exchange rate determines how much the dosimeter's response changes with each 3 dB increase in sound level. This specific exchange rate is commonly used in occupational noise exposure assessments and is consistent with Air Force standards. It allows for accurate measurement and comparison of noise levels to ensure compliance with safety regulations and protect the hearing health of Air Force personnel.

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• 22.

### (415) When would be considered the most appropriate time to conduct a noise dosimetry survey?

• A.

Just before or after a weekend

• B.

During a workplace inspection

• C.

If the workload is temporarily increased

• D.

When workdays are representative of normal shifts

D. When workdays are representative of normal shifts
Explanation
The most appropriate time to conduct a noise dosimetry survey would be when workdays are representative of normal shifts. This means that the survey should be conducted during regular working hours, when employees are performing their usual tasks and the noise levels are typical of their everyday work environment. Conducting the survey during this time will provide the most accurate assessment of noise exposure and help in determining the necessary measures to protect employees from excessive noise levels.

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• 23.

### (416) How many meadurements do you take with an octave band analyzer during a survey?

• A.

5

• B.

7

• C.

10

• D.

12

C. 10
Explanation
During a survey with an octave band analyzer, 10 measurements are taken. This is because an octave band analyzer divides the frequency range into 10 different bands, each with a specific frequency range. By taking measurements in each of these 10 bands, a comprehensive analysis of the sound or noise can be obtained.

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• 24.

### (417) How often are audiometric test booths monitored?

• A.

Monthly

• B.

Annually

• C.

Quarterly

• D.

Bi-annually

B. Annually
Explanation
Audiometric test booths are monitored on an annual basis. This means that they are checked and evaluated once every year. This regular monitoring ensures that the booths are functioning properly and meeting the required standards for conducting audiometric tests. It allows for any necessary maintenance or repairs to be carried out to ensure accurate and reliable test results. Monitoring the booths annually helps to maintain the quality and effectiveness of the testing environment.

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• 25.

### (418) Noise dosimeters that indicate the daily dose as a percentage need to be converted to the

• A.

Compliance factor

• B.

Time weighted average

• C.

Average daily exposure

• D.

Daily equivalent sound level

D. Daily equivalent sound level
Explanation
Noise dosimeters that indicate the daily dose as a percentage need to be converted to the daily equivalent sound level. This is because the daily equivalent sound level provides a measure of the overall sound exposure over a 24-hour period, taking into account both the intensity and duration of the noise. It is a more comprehensive metric for assessing noise exposure and is commonly used in occupational health and safety regulations to determine compliance with noise exposure limits.

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• 26.

### (419) What is the most preferred method of identifying hazardous noise areas?

• A.

Noise dosimetry

• B.

Sound level meter survey

• C.

Audiometric booth testing

• D.

Impulse noise measurements

A. Noise dosimetry
Explanation
Noise dosimetry is the most preferred method of identifying hazardous noise areas because it provides a more accurate and comprehensive assessment of noise exposure over a period of time. It measures the cumulative noise exposure received by an individual throughout the workday, taking into account both continuous and intermittent noise sources. This method allows for the identification of high-risk areas and individuals who may be at risk of developing hearing loss or other noise-related health issues. Sound level meter surveys, audiometric booth testing, and impulse noise measurements may provide valuable information, but they are not as effective in capturing the full extent of noise exposure in a real-world setting.

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• 27.

### (420) When a sound level meter is used and levels are changing, how often should readings be taken over the period of interest in order to obtain a 95% confidence level?

• A.

Every 60 seconds

• B.

Every 45 seconds

• C.

Every 20 seconds

• D.

Every 10 seconds

D. Every 10 seconds
Explanation
In order to obtain a 95% confidence level when using a sound level meter, readings should be taken every 10 seconds. This frequency allows for a more accurate representation of the changing sound levels over the period of interest. By taking readings more frequently, any fluctuations or variations in the sound levels can be captured, leading to a higher level of confidence in the measurements obtained.

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• 28.

### (421) You are evaluating an administrative area for speech interferences and you determine that a normal voice can be heard from 6-12 feet. What would be the range of noise levels in this environment?

• A.

50-60 dB(A)

• B.

45-50 dB(A)

• C.

40-45 dB(A)

• D.

30-40 dB(A)

B. 45-50 dB(A)
Explanation
In this question, the range of noise levels in the environment is being evaluated based on the fact that a normal voice can be heard from 6-12 feet. Since a normal conversation typically ranges from 45-50 dB(A), it can be inferred that the noise levels in this environment would fall within that range. Therefore, the correct answer is 45-50 dB(A).

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• 29.

### (422) What type of path control is the most appropriate for reducing noise transmitted by a large machine throughout a building structure?

• A.

Reduce the driving force

• B.

Isolate the source from the structure

• C.

Use damping to reduce surface response

• D.

Build a barrier wall to enclose the source

D. Build a barrier wall to enclose the source
Explanation
Building a barrier wall to enclose the source is the most appropriate type of path control for reducing noise transmitted by a large machine throughout a building structure. By enclosing the source of the noise with a barrier wall, the sound waves are prevented from traveling freely and spreading throughout the building. This containment helps to reduce the overall noise levels and prevents it from propagating to other areas of the structure.

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• 30.

### (423) What is the most preferred method available to determine attenuation factors for hearing protection devices?

• A.

Octave band

• B.

Noise dosimetry

• C.

C-A calculation method

• D.

Noise reduction rating method

A. Octave band
Explanation
The most preferred method available to determine attenuation factors for hearing protection devices is octave band. This method involves measuring the sound attenuation provided by the device across different frequency bands. By analyzing the attenuation at different frequencies, the effectiveness of the device can be assessed more accurately. This method is widely used in the field of audiology and is considered to be more reliable in determining the level of protection provided by hearing protection devices.

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