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OHST practice questions

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Question 1Safety and Health Program Management

Which element is most essential to the success of a workplace safety and health program?

  1. Detailed written job descriptions for each employee
  2. Safety poster campaigns posted in break areas
  3. Visible management commitment and leadership Correct answer.
  4. A large budget allocated to new equipment

Explanation

Management commitment drives every other program element, because leaders set policy, assign resources, and hold people accountable for results. Programs without visible leadership support typically lose momentum and their hazard controls erode over time.

Question 2Safety and Health Program Management

According to the hierarchy of controls, which measure is the most effective way to reduce a hazard?

  1. Posting warning signs near the hazard location
  2. Providing personal protective equipment to affected workers
  3. Training employees to recognize the hazard
  4. Eliminating the hazard from the workplace entirely Correct answer.

Explanation

The hierarchy of controls ranks measures from most to least effective: elimination, substitution, engineering controls, administrative controls, and personal protective equipment. Elimination removes the hazard so that exposure becomes impossible, which makes it the most reliable option.

Question 3Safety and Health Program Management

What is the primary purpose of a workplace safety self-inspection?

  1. To satisfy insurance carrier paperwork
  2. To determine which employee was at fault
  3. To identify hazards before they cause injury Correct answer.
  4. To replace the need for outside consultants

Explanation

A self-inspection is a planned walkthrough that finds unsafe conditions and practices so they can be corrected before anyone is harmed. Findings feed the hazard control process rather than a fault-finding exercise.

Question 4Safety and Health Program Management

Which function is typical of a joint labor-management safety committee?

  1. Setting the annual operating budget for the facility
  2. Issuing disciplinary citations to employees who violate rules
  3. Reviewing inspection findings and recommending controls Correct answer.
  4. Providing medical treatment to injured workers

Explanation

Joint committees typically review inspection results, injury trends, and worker concerns, then recommend corrective actions to management. They generally do not carry out discipline, budgeting, or medical treatment.

Question 5Safety and Health Program Management

Under OSHA recordkeeping rules, within how many days must an employer record a work-related injury or illness on the OSHA 300 log?

  1. Twenty-four hours after the incident
  2. Seven calendar days after learning of it Correct answer.
  3. Thirty days after the close of the year
  4. Forty-eight hours after medical treatment

Explanation

OSHA requires employers to enter a recordable injury or illness on the OSHA 300 log within seven calendar days after learning of it. Separate rules require reporting fatalities to OSHA within eight hours and certain severe injuries within twenty-four hours.

Question 6Safety and Health Program Management

What is the main goal of an incident investigation?

  1. Determining which employee was at fault
  2. Identifying root causes to prevent recurrence Correct answer.
  3. Documenting costs for the insurance claim
  4. Meeting the reporting deadline for regulators

Explanation

Investigations look past the immediate event to the underlying management and design failures that allowed it, so corrective actions can prevent a repeat. Blame-focused investigations suppress reporting and leave root causes in place.

Question 7Safety and Health Program Management

Why should employees participate in developing a safety and health program?

  1. It transfers legal liability to the workers
  2. It removes the need for written procedures
  3. It eliminates the requirement for training
  4. Workers know the tasks and their hazards Correct answer.

Explanation

Employees who perform the task daily notice changes, near misses, and workarounds that managers and auditors often miss. Their involvement also builds ownership of the controls that are selected.

Question 8Safety and Health Program Management

Safety and health training is most effective when it is:

  1. Delivered in a language workers understand Correct answer.
  2. Conducted only after an injury has occurred
  3. Delivered once during new-hire orientation only
  4. Focused only on penalties for rule violations

Explanation

Training must be understandable to the workers receiving it, which means using language, vocabulary, and literacy levels they can follow. One-time, punishment-focused, or after-the-fact sessions do not build the skills needed to recognize and control hazards.

Question 9Safety and Health Program Management

Which practice best builds safety accountability among supervisors?

  1. Waiting for injuries before corrective action
  2. Relying on informal peer pressure between workers
  3. Posting generic slogans around the facility
  4. Reviewing safety results in supervisor appraisals Correct answer.

Explanation

Accountability is built when safety duties are written into job expectations and measured in performance reviews, so supervisors see safety as part of the job rather than an extra. Waiting for injuries or relying on slogans does not create measurable responsibility.

Question 10Safety and Health Program Management

A job hazard analysis breaks a job down into:

  1. Successive steps so hazards can be spotted Correct answer.
  2. The wage rates paid for each part of the work
  3. The tools purchased during the past fiscal year
  4. The headcount needed on each production shift

Explanation

A job hazard analysis lists the steps of a task in sequence and identifies the hazards associated with each step, which then point to appropriate controls. Pay rates, staffing levels, and purchasing records are unrelated to the technique.

Question 11Safety and Health Program Management

Which of the following is a leading indicator of safety performance?

  1. Lost workdays recorded during the last quarter
  2. Percent of scheduled inspections completed Correct answer.
  3. Workers' compensation claim costs to date
  4. Recordable injury count for the calendar year

Explanation

Leading indicators measure preventive activities, such as completing planned inspections, delivering training, or closing corrective actions, and they change before injuries occur. Injury counts, claim costs, and lost days are lagging indicators that describe harm already done.

Question 12Safety and Health Program Management

Which approach best evaluates whether a safety and health program is effective?

  1. Counting the number of safety posters displayed
  2. Comparing trend data against goals and audits Correct answer.
  3. Asking managers whether they feel the program works
  4. Reviewing only the injury rate for the current year

Explanation

Effectiveness is judged by combining trend data on injuries and exposures with progress toward stated goals and the results of audits and inspections. A single year's rate, informal opinions, or activity counts are too narrow to support that judgment.

Question 13Safety and Health Program Management

Before installing a new piece of production equipment, a safety professional should:

  1. Assume the vendor has addressed all safety issues
  2. Assess how the change affects hazards and controls Correct answer.
  3. Wait until after startup to see if problems appear
  4. Notify the insurance carrier and take no other action

Explanation

Management of change requires that new equipment, processes, or materials be reviewed for their safety impact before they are introduced, so hazards are controlled at the source. Waiting for startup problems or trusting the vendor leaves the host employer responsible for unaddressed risks.

Question 14Safety and Health Program Management

Which practice best protects host-site workers when contractors perform work on site?

  1. Requiring contractors to sign a liability waiver
  2. Exchanging hazard information before work begins Correct answer.
  3. Allowing contractors to follow only their own rules
  4. Assigning contractors to the host's break areas only

Explanation

Host and contractor employers must exchange information about site hazards, controls, and emergency procedures before work starts, so each party can protect the workers it directs. Liability waivers and seating arrangements do not address exposure.

Question 15Safety and Health Program Management

A safety professional notices that injuries cluster in one department. The best next step is to:

  1. Reassign the department supervisor to another area
  2. Assume the cluster is random variation and monitor it
  3. Wait for another injury before investigating causes
  4. Examine that department's tasks and controls Correct answer.

Explanation

A cluster of injuries in one area suggests a shared cause, such as similar tasks, equipment, or supervision, so the work and its controls should be examined there. Treating the pattern as random or waiting for another injury delays correction.

Question 16Safety and Health Program Management

A formal return-to-work program primarily helps by:

  1. Encouraging injured employees to remain off work longer
  2. Reducing the need for hazard controls at the site
  3. Keeping injured workers productive during recovery Correct answer.
  4. Shifting medical costs to the injured employee

Explanation

Return-to-work programs place recovering employees in productive, medically appropriate duties, which maintains skills and morale and often shortens lost time. They do not remove the employer's duty to control hazards or shift costs to the worker.

Question 17Safety and Health Program Management

Which feature most encourages workers to report hazards without fear?

  1. A suggestion box that is emptied once a year
  2. A policy of disciplining workers who report hazards
  3. Requiring written reports to be signed by a supervisor
  4. A no-blame reporting process with timely feedback Correct answer.

Explanation

Workers report hazards when they expect their report to be taken seriously and acted on, and when reporting does not expose them to punishment. Delayed or burdensome reporting channels discourage use.

Question 18Safety and Health Program Management

How can a safety professional best verify that training was effective?

  1. Counting the number of attendees who signed in
  2. Filing the training rosters in the office records
  3. Observing trained behaviors on the job Correct answer.
  4. Reviewing the instructor's lesson plan for accuracy

Explanation

The test of training is whether behavior changes on the job, which requires observing workers performing the task. Attendance counts, filed rosters, and lesson plans document activity rather than learning.

Question 19Safety and Health Program Management

A worker slipped on an oily floor. Which finding represents a root cause rather than an immediate cause?

  1. The spill occurred at approximately 2:15 p.m.
  2. The floor surface was covered with spilled oil
  3. Maintenance schedules were never followed Correct answer.
  4. The worker was wearing smooth-soled shoes

Explanation

A root cause is the underlying system failure that permitted the incident, such as a maintenance program that was not carried out. The oil on the floor, the footwear, and the time of day describe the immediate circumstances of the event.

Question 20Safety and Health Program Management

A safety manager wants to reduce noise exposure at a stamping press. Which control should be considered first?

  1. Posting a warning sign at the press entrance
  2. Rotating operators to limit their exposure time
  3. Issuing hearing protection devices to the press operators
  4. Installing an acoustical enclosure around the press Correct answer.

Explanation

Engineering controls that reduce noise at the source are preferred under the hierarchy of controls because they protect every exposed worker without relying on behavior. Hearing protection and rotation are lower-level measures used when source controls are not feasible.

Question 21Safety and Health Program Management

A safety and health program is most likely to remain effective when top management:

  1. Reviews program results and acts on them regularly Correct answer.
  2. Reviews the program only after a serious injury occurs
  3. Delegates all safety decisions to first-line supervisors
  4. Approves the program once and then leaves it unchanged

Explanation

Continuing effectiveness depends on a cycle in which management reviews results, sets priorities, and commits resources at planned intervals. Delegating all decisions, approving once, or acting only after serious harm breaks that cycle.

Question 22Safety and Health Program Management

A safety professional is asked to review plans for a new facility. The greatest opportunity to prevent future injuries is during:

  1. The design and planning phase of the project Correct answer.
  2. The first year of full production operation
  3. The first scheduled audit after startup begins
  4. The final walkthrough before occupancy

Explanation

Prevention through design holds that the greatest risk reduction comes when hazards are designed out during planning, before equipment and processes are fixed in place. Later phases offer fewer options and greater cost to make changes.

Question 23Safety and Health Program Management

Which safety objective is written in a measurable, verifiable form?

  1. Encourage everyone to work more safely
  2. Improve overall safety culture throughout the year
  3. Make the warehouse a safer place to work
  4. Cut forklift near-misses 25% by June 30 Correct answer.

Explanation

A verifiable objective states a measurable result and a deadline, so progress can be tracked and success can be judged. General statements about improving culture or being safer cannot be measured.

Question 24Safety and Health Program Management

Which statement best distinguishes a safety audit from a routine safety inspection?

  1. An audit evaluates the whole management system Correct answer.
  2. An audit is performed only by hourly employees
  3. An audit focuses only on physical conditions
  4. An audit is conducted only after an injury occurs

Explanation

An audit examines the management system, including policies, responsibilities, training, and follow-up, to judge whether the program as a whole is working. An inspection typically checks physical conditions and work practices against standards.

Question 25Safety and Health Program Management

A company's injury rate is below its industry average, yet workers say many near misses go unreported. What does this most likely indicate?

  1. The program has eliminated all workplace hazards
  2. The injury rate should be disregarded as unreliable
  3. Near misses are unrelated to future injury potential
  4. Underreporting is hiding uncontrolled hazards Correct answer.

Explanation

A low injury rate combined with widespread unreported near misses suggests that reporting is suppressed, so hazards persist unrecognized and uncontrolled. Near misses are useful warning events that often precede more serious incidents.

Question 26Safety and Health Program Management

An organization's written safety and health policy statement is most useful when it:

  1. commits top management to protecting workers and is signed by a senior executive Correct answer.
  2. catalogs every hazard in the plant along with the specific control chosen for each one
  3. is kept in the safety office so that supervisors can consult it when questions arise
  4. is revised only when a regulatory inspector asks to see a current copy of it

Explanation

A policy statement is a short, top-level expression of management's commitment and objectives that sets direction for the whole program, and it carries the signature of the most senior executive to give it authority. It is meant to be communicated to all workers, not filed away. Detailed hazard inventories and control decisions belong in hazard assessments and job hazard analyses, not in the policy.

Question 27Safety and Health Program Management

Which statement best describes a safety and health program?

  1. an integrated set of policies, procedures, and practices to prevent injury Correct answer.
  2. the set of personal protective equipment issued to each worker on a job
  3. the checklist a supervisor uses during a weekly walkthrough of the area
  4. the training records and certifications kept in each employee's file

Explanation

A safety and health program is a systematic, integrated set of policies, procedures, responsibilities, and practices aimed at preventing injury and illness rather than a single tool or record set. Individual items such as PPE, training records, and inspection checklists are components that support the program.

Question 28Safety and Health Program Management

A joint labor-management safety committee is most effective when it:

  1. reviews hazards and near misses and tracks the response to each Correct answer.
  2. meets only after a serious injury occurs so that meetings stay short
  3. is composed exclusively of managers so that discussion stays efficient
  4. focuses on assigning discipline after incidents are reported by supervisors

Explanation

The value of a joint committee lies in ongoing, two-way review of hazards, near misses, and worker suggestions, with follow-up so that recommendations actually close out. Meeting only episodically or excluding workers removes the perspective the committee exists to provide. Discipline is a line management function, not the committee's purpose.

Question 29Safety and Health Program Management

The primary purpose of an emergency action plan is to:

  1. satisfy the reporting requirements set by the company's insurance carrier
  2. document the facility's injury and illness rates for the past calendar year
  3. assign responsibility for errors made during an evacuation or drill
  4. describe how workers should respond, evacuate, and be accounted for Correct answer.

Explanation

An emergency action plan establishes what workers must do when an emergency occurs, including reporting, evacuation routes, assembly, accounting for personnel, and rescue duties. It is an operational document prepared before an event, not a statistical summary or a fault-finding exercise.

Question 30Safety and Health Program Management

Before selecting personal protective equipment for a task, OSHA requires the employer to:

  1. wait until an injury shows which body parts are at risk
  2. ask each worker to choose the equipment that they prefer
  3. obtain the manufacturer's catalog and price list for each item
  4. perform and document a hazard assessment of the workplace Correct answer.

Explanation

The PPE standard requires the employer to assess the workplace to determine whether hazards necessitate PPE, and to certify in writing that the hazard assessment was performed, identifying the workplace evaluated, the certifier, and the date. Selection then follows from the hazards identified.

Question 31Safety and Health Program Management

A site recorded 6 OSHA recordable cases while employees worked 300,000 hours during the year. What is the total recordable incident rate (TRIR) per 100 full-time-equivalent workers?

  1. 6.0
  2. 2.0
  3. 4.0 Correct answer.
  4. 12.0

Explanation

The rate is calculated as (number of recordable cases x 200,000) / hours worked, where 200,000 represents 100 workers at 40 hours per week for 50 weeks. For this site, (6 x 200,000) / 300,000 = 4.0 recordable cases per 100 full-time-equivalent workers.

Question 32Safety and Health Program Management

A production line will begin using a new solvent-based adhesive. Which action best applies management of change?

  1. assess the new hazards and update procedures and training before startup Correct answer.
  2. rely on the supplier's safety data sheet to cover any hazards the change creates
  3. distribute respirators to the affected workers on the day production starts
  4. add the new adhesive to the approved chemical list after the first batch is used

Explanation

Management of change is a formal process for recognizing the hazards introduced by a change in chemicals, equipment, processes, or staffing and controlling them before the change is implemented, including revised procedures, training, and authorization. Reviewing hazards after the first batch has run defeats the purpose of the process.

Question 33Safety and Health Program Management

A safety incentive program offers a monthly bonus to crews with no reported injuries. What is the main risk of this design?

  1. it rewards crews that work in low-hazard areas regardless of effort
  2. it can discourage workers from reporting injuries and near misses Correct answer.
  3. it generally costs more than the injuries it prevents
  4. it can only be applied to managers rather than to hourly workers

Explanation

An incentive tied to the number of reported injuries rewards the absence of reports rather than the absence of hazards, creating pressure to hide injuries and near misses and to delay treatment. Safer designs reward participation in hazard identification, reporting, and correction.

Question 34Safety and Health Program Management

When a safety professional must decide which of several identified hazards to address first, the most defensible basis is:

  1. the order in which the hazards appear on the inspection form
  2. the hazard that employees complained about most recently
  3. the hazard whose control is least expensive to purchase
  4. an estimate of severity combined with likelihood of harm Correct answer.

Explanation

Risk is conventionally estimated as a function of the severity of the potential harm and the probability that it will occur, and ranking hazards on that basis concentrates limited resources where risk is greatest. Cost and feasibility are considered when choosing among controls, not as the primary driver of priority.

Question 35Safety and Health Program Management

Under OSHA's lockout/tagout standard, the periodic inspection of energy control procedures must be performed:

  1. each month, by the plant safety committee chairperson
  2. whenever a new machine is installed, by the maintenance planner
  3. only after a lockout-related injury, by the affected line supervisor
  4. at least annually, by an authorized employee not using the procedure Correct answer.

Explanation

The standard requires a periodic inspection of each energy control procedure at least annually, conducted by an authorized employee other than the one using the procedure, to correct any deviations or deficiencies found. It also requires that the inspection cover both the procedure and the employees' understanding of it.

Question 36Safety and Health Program Management

Which element is required in a written respiratory protection program when respirators are necessary to protect employees?

  1. purchase of the most expensive filter available for the hazard
  2. voluntary use of respirators by all employees in the facility
  3. annual fit testing only for employees who request it
  4. medical evaluation of employees before fit testing and use Correct answer.

Explanation

The respiratory protection standard requires that employees be medically evaluated before fit testing or use and be medically cleared to wear a respirator. The written program must also address selection, fit testing, training, maintenance, and program evaluation.

Question 37Safety and Health Program Management

OSHA's Recommended Practices for Safety and Health Programs identify which of the following as a core element?

  1. worker participation in finding and controlling hazards Correct answer.
  2. purchase of incentive merchandise such as jackets and gift cards
  3. annual submission of the injury and illness logs to OSHA for review
  4. mandatory drug testing of every employee before each shift

Explanation

Worker participation is one of the core elements of a safety and health program, along with management leadership, hazard identification and assessment, hazard prevention and control, education and training, program evaluation and improvement, and coordination with contractors and staffing agencies. Participation means workers are involved in identifying hazards and shaping solutions.

Question 38Safety and Health Program Management

The OSHA Form 300A annual summary must be posted:

  1. from January 1 through December 31 of the record year
  2. only when an OSHA compliance officer requests to see it
  3. for 30 days after the last recordable case of the year
  4. from February 1 through April 30 of the following year Correct answer.

Explanation

The annual summary must be completed and posted no later than February 1 and kept posted in a conspicuous place through April 30 of the year following the record year. Posting is how employees are informed of the establishment's injury and illness experience.

Question 39Safety and Health Program Management

Under OSHA's rule on access to employee exposure and medical records, an employee's request for exposure records must be granted:

  1. within 30 calendar days of the written request
  2. at the end of the calendar year in which the exposure occurred
  3. within 15 working days of the request Correct answer.
  4. within 60 days, and only if the employee pays copying costs

Explanation

The access rule requires the employer to provide employees and their designated representatives access to exposure and medical records within 15 working days of the request, at no cost to the employee. Analyses using exposure or medical records must be provided as well.

Question 40Safety and Health Program Management

Which document is an international, third-party certifiable standard for an occupational health and safety management system?

  1. OSHA 29 CFR 1910
  2. NFPA 70E
  3. ANSI/ASSP Z10
  4. ISO 45001 Correct answer.

Explanation

ISO 45001 specifies requirements for an occupational health and safety management system and organizations can have their systems audited and certified by third parties against it. It follows the same high-level management system structure as other ISO standards, which supports integration with quality and environmental systems.

Question 41Occupational Health and Industrial Hygiene

Under OSHA's noise exposure standard, a hearing conservation program must be established for employees whose 8-hour time-weighted average exposure equals or exceeds which level?

  1. 80 dBA
  2. 95 dBA
  3. 90 dBA
  4. 85 dBA Correct answer.

Explanation

The hearing conservation amendment sets an action level of 85 dBA as an 8-hour TWA, while the permissible exposure limit itself is 90 dBA. Reaching the action level obligates the employer to provide monitoring, audiometric testing, training, and hearing protection.

Question 42Occupational Health and Industrial Hygiene

A Threshold Limit Value-Short-Term Exposure Limit (TLV-STEL) is a 15-minute time-weighted average that, by ACGIH convention, should be exceeded no more than how many times per workday?

  1. Six times
  2. Eight times
  3. Two times
  4. Four times Correct answer.

Explanation

ACGIH defines the STEL as a 15-minute TWA that should not be exceeded at any time during the workday, with no more than four excursions per day and at least 60 minutes between successive excursions. The STEL supplements rather than replaces the 8-hour TLV-TWA.

Question 43Occupational Health and Industrial Hygiene

OSHA considers an atmosphere oxygen deficient when the oxygen concentration falls below what level?

  1. 21.0 percent
  2. 19.5 percent Correct answer.
  3. 16.0 percent
  4. 18.0 percent

Explanation

Confined space practice reflected in OSHA's permit-required confined space standard treats 19.5 percent oxygen as the lower bound of a safe atmosphere and 23.5 percent as the upper bound because of fire risk. Values outside that range require ventilation and re-testing before entry.

Question 44Occupational Health and Industrial Hygiene

Under OSHA's asbestos standard, the permissible exposure limit as an 8-hour time-weighted average is which of the following?

  1. 1.0 fiber per cubic centimeter
  2. 0.1 fiber per cubic centimeter Correct answer.
  3. 0.5 fiber per cubic centimeter
  4. 5.0 fibers per cubic centimeter

Explanation

29 CFR 1910.1001 sets the 8-hour TWA PEL at 0.1 f/cc and a separate excursion limit of 1.0 f/cc averaged over 30 minutes. The excursion limit prevents brief high peaks even when the 8-hour average is compliant.

Question 45Occupational Health and Industrial Hygiene

OSHA's permissible exposure limit for respirable crystalline silica in general industry is which 8-hour time-weighted average?

  1. 50 micrograms per cubic meter Correct answer.
  2. 25 micrograms per cubic meter
  3. 10 micrograms per cubic meter
  4. 100 micrograms per cubic meter

Explanation

The 2016 silica standard lowered the 8-hour TWA PEL to 50 micrograms per cubic meter of respirable crystalline silica and set an action level of 25 micrograms per cubic meter. Reaching the action level triggers exposure monitoring and related program elements.

Question 46Occupational Health and Industrial Hygiene

For occupational exposure to ionizing radiation, the annual whole-body dose limit for a radiation worker is which of the following?

  1. 50 rem (500 mSv)
  2. 1.25 rem (12.5 mSv)
  3. 5 rem (50 mSv) Correct answer.
  4. 15 rem (150 mSv)

Explanation

The occupational total effective dose equivalent limit is 5 rem (50 mSv) per year. Separate and generally higher limits apply to the lens of the eye and to the extremities and skin, while lower limits apply to members of the public and to a declared fetus.

Question 47Occupational Health and Industrial Hygiene

Which heat stress index combines dry-bulb, natural wet-bulb, and globe temperature into a single number that can be compared with a threshold limit value?

  1. Heat index
  2. Humidex
  3. WBGT Correct answer.
  4. Effective temperature

Explanation

Wet bulb globe temperature weights the three readings differently depending on whether the exposure is indoors or in direct sunlight, and ACGIH expresses its heat stress TLVs in WBGT. A heat index, by contrast, is derived from temperature and humidity alone.

Question 48Occupational Health and Industrial Hygiene

Combustible gas indicators used for permit-required confined space entry are typically set to alarm at what percentage of the lower explosive limit?

  1. 25 percent
  2. 1 percent
  3. 10 percent Correct answer.
  4. 50 percent

Explanation

Entry practice treats 10 percent of the LEL as the action level at which testing stops, ventilation is increased, and re-entry is prohibited until readings fall below it. This maintains a wide margin below the concentration at which ignition becomes possible.

Question 49Occupational Health and Industrial Hygiene

Using OSHA's 5-dB exchange rate, what is the maximum permissible exposure duration at a continuous noise level of 100 dBA?

  1. 2 hours Correct answer.
  2. 4 hours
  3. 1 hour
  4. 30 minutes

Explanation

The permissible duration halves with each 5-dB increase above 90 dBA: eight hours at 90, four hours at 95, and two hours at 100. Exposures beyond two hours at 100 dBA require hearing protection and may call for engineering controls.

Question 50Occupational Health and Industrial Hygiene

Compared with dilution ventilation, local exhaust ventilation is the preferred control for airborne contaminants because it...

  1. relies on general room air mixing
  2. requires no exhaust ductwork or fan
  3. dilutes the contaminant with large air volumes
  4. captures the contaminant at its source Correct answer.

Explanation

Local exhaust captures contaminant at the point of generation before it can enter the breathing zone, protecting the worker with far less air than dilution would require. Dilution depends on good mixing and suits only low-toxicity contaminants released at a fairly uniform rate.