Silica facts

Pulmonary Function Testing

What is Pulmonary Function Testing?

Pulmonary function testing is not a single test, but rather, a series of maneuvers aimed at evaluating the functioning of the lungs. This testing may also be referred to as PFTs, lung function testing, spirometry, or breathing tests. Pulmonary function testing generally consists of 3 components:

  1. Spirometry– measuring how much air you exhale and how quickly, which can help evaluate for a broad range of diseases, including asthma
  2. Lung Volumes- measuring the amount of air in your lungs can help in evaluating diseases like emphysema (generally too much air) or scarring diseases like asbestosis (generally too little air)
  3. Diffusion Capacity (DLCO)- measuring how well your lungs can bring oxygen into the bloodstream can help in evaluating a number of lung diseases, including the category called interstitial lung disease

Other possible components include bronchodilator testing (generally repeating spirometry after giving you an inhaled medication to open your airways), ventilation maximums (to assess neuromuscular function), exercise stress testing (testing heart and lungs during exercise), arterial blood gases, and inhalation challenge (testing before and after administering an inhaled substance that produces an asthma-like reaction in certain conditions).

Why did my doctor order PFTs?

  • To help in the evaluation of shortness of breath or other signs or symptoms of lung disease
  • To screen those at risk for lung disease, such as smokers or ex-smokers or those exposed to certain substances
  • For disability/impairment evaluations
  • To assess prognosis and monitor disease progression
  • To determine lung condition before surgery (especially for those undergoing chest or major surgery), and assess the risk of respiratory complications during and after surgery
  • To measure the effect of a disease on lung function (including non-lung diseases)
  • To monitor the effect of medication and to evaluate treatment response

How is the testing done?

Most testing is performed in a comfortable, seated position. Testing might take up to one hour, depending upon the testing ordered. The technician will repeat tests in order to obtain your “best” results. You will have a chance to rest between test trials. You will breathe into a mouthpiece, while wearing nose clips to ensure no air passes in or out of your nose during the test.

For spirometry, you will breathe into the mouthpiece that is connected to an instrument called a spirometer. The spirometer records the amount and the rate of air that you breathe in and out over a period of time. For some of the test measurements, you will breathe normally and quietly. Other tests require forced exhalation after a deep and full breath.

NIOSH has a certification program for spirometry technician training, to assure that spirometries performed in the occupational setting are properly conducted and standardized. Technicians who have passed a NIOSH-certified training course are required by the new OSHA silica standards.

Lung volume measurement can be done in two ways:

  • The most accurate way is to sit in a sealed, clear box (body plethysmograph or “body box”) that looks like a telephone booth with windows, while breathing in and out or panting into a tightly sealed mouthpiece. Changes in pressure inside the box help determine the lung volumes.
  • Lung volumes can also be measured when you breathe nitrogen or helium gas through a tube for a certain period of time. The concentration of the gas in a chamber attached to the tube is measured to estimate the lung volume.

To measure diffusion capacity, you breathe a harmless gas for a very short time, and then hold your breath for about 10 seconds. The concentration of the gas in the air you breathe out then is measured. The difference in the amount of gas inhaled and exhaled can help estimate how quickly gas can travel from the lungs into the blood.

Are there any risks?

This is a painless test, with little or no risk for most people. Since the test involves some forced breathing and rapid breathing, you may have some temporary shortness of breath or light-headedness. There is a very small risk of collapsed lung in people with a certain type of lung disease. The risks are greater in those who have experienced a recent (within the past month) heart attack, have certain other types of heart disease, are experiencing current heart pains, patients with severe high blood pressure, or those having undergone recent eye surgery. Abdominal pains, facial or mouth pain, confusion, or recent stroke can interfere with optimal and reliable results. Certain medications (such as beta blockers or certain asthma medicines) can also interfere with results. The physician or PFT technician should be made aware of any condition that might adversely affect the results or pose a risk to the examinee.

What can I do?

Your cooperation while performing the test is crucial in order to get accurate and reliable results. It is important to have a tight seal around the mouthpiece. If you have dentures, wearing them during the test is preferred. Wear loose, comfortable clothing. Take your regular medications, unless otherwise instructed by your doctor, and bring in a list of your medicines.

Testing subjects should preferably avoid certain activities before testing. These include:

  • smoking within one hour before the test (preferably not at all on the day of testing)
  • consuming alcohol within 4 hours of testing
  • eating a large meal within 2 hours of testing
  • performing vigorous activity within 30 minutes of testing
  • wearing constrictive clothing

How does the doctor grade the test?

Expected (or “predicted”) values are based upon your age, height, sex, and ethnicity. The predicted values may vary slightly among different laboratories.

Generally, your results will be compared to the predicted values for someone just like you. Depending upon the parameter, a value will be considered abnormal if it is less than a certain percentage of your predicted value (often 80%). Some testing provides a “lower limit of normal” and your result would be abnormal if you fall below that level.

Abnormal results may mean that you have some chest or lung disease. Talk to your doctor about the meaning of your specific test results.

Spirometry by NIOSH-certified technicians is required for compliance with OSHA’s new silica surveillance and screening guidelines.

Where can I find out more information:

American Lung Association

American Thoracic Society guidelines

NIOSH Spirometry Guidelines

Silicosis 101

Silicosis is a term describing pneumoconiosis (“dust disease of the lung”) caused by inhalation of dust containing respirable particles (< 10 µm in diameter) of crystalline silica.

Silica refers to silicon dioxide (SiO2), which occurs in crystalline or non-crystalline (amorphous) form. There are different forms of crystalline silica, including alpha quartz (“quartz”), which is the most common. Rock and soil commonly contain quartz. Other forms of crystalline silica, cristobalite and tridymite, are also found in soil and rock and can occur from heating alpha quartz or amorphous silica. Silica is the main part of sand. These three silica polymorphs are the most important in causing silicosis.

Silicosis has been recognized since antiquity. With the introduction of mechanical mining or other activities rupturing rock or sand into fine dust, the prevalence of silicosis increased. The risk of silicosis increases with dose (related to the intensity and duration of exposure) of respired crystalline silica. In the US, an estimated 1-2 million workers have had occupational exposure to crystalline silica dust. The precise number of those with silicosis, however, is not known. In recent decades in the US, the mortality rate from silicosis has been declining, suggesting recognition of hazards and more effective industrial hygiene measures.

People who work in jobs that expose them to silica dust are at increased risk for getting silicosis. These jobs include:

  1. mining, quarrying, tunneling and drilling
  2. abrasive blasting using silica-containing material (such as sandblasting)
  3. stone cutting and tombstone worker
  4. foundry worker
  5. refractory brick worker
  6. pottery worker

There are three basic types of silicosis:

  1. Chronic simple silicosis- usually resulting from long-term exposure (10-20 or more years) to lower concentrations of silica dust. This is the most common variety.
  2. Accelerated silicosis- which occurs 5-10 years after first exposure to larger amounts of silica dust.
  3. Acute silicosis- developing within a period of a few weeks to 5 years after exposure to high concentrations of respirable crystalline silica dust.

Silicosis can become “complicated” by the development of severe scarring (progressive massive fibrosis, or PMF) or by other disease, such as tuberculosis. Silicotics also have an increased risk for other Mycobacterial infections and fungal lung infections. Complicated silicosis is more common with accelerated silicosis than with the chronic variety. Silica is considered a human carcinogen, and persons with silicosis are at increased risk for lung cancer.

Symptoms of chronic silicosis include cough and shortness of breath (especially with exertion). Many in the early stages have no symptoms.  Some patients may experience weight loss, fatigue, or fever. Call your physician if you have been exposed to silica at work and you have symptoms of the disease.

The clinical diagnosis rests upon a thorough occupational and medical history, physical examination, x-ray and exclusion by your doctor of other potential diseases. The non-acute forms are marked by inflammation and scarring, in the form of small nodules, primarily in the upper lobes of the lungs. There may be enlargement of lymph nodes in the chest, sometimes with characteristic “egg-shell” pattern. Often your doctor will obtain pulmonary function tests (PFTs) to assess the impact of silicosis on lung functioning. Only rarely is lung biopsy required.

There is no known cure for silicosis. Acute silicosis may sometimes be treated with whole lung lavage, but this usually does not decrease the mortality of this severe variety of silicosis. After being diagnosed, you should have a baseline TB skin test (PPD) and if not positive (< 10mm induration), it should be repeated about every two years. For those with a positive PPD, one year of isoniazid prophylaxis is recommended. For those with active tuberculosis, the treatment is usually prolonged and may still lead to recurrent TB. Patients with silicosis who smoke should stop smoking. In the absence of effective treatment, primary prevention (control of exposure to respirable crystalline silica) is the only reasonable approach.

OSHA has recently adopted new guidelines for surveillance (screening) of workers who are exposed to silica regularly.


  1. World Health Organization (WHO) – Silicosis fact sheet
  2. Occupational and Safety Health Administration (OSHA) – Safety and health topics, silica, crystalline
  3. American Thoracic Society (ATS) 1996 statement – Adverse effects of crystalline silica exposure
  4. Centers for Disease Control (CDC)/ National Institute for Occupational Safety and Health (NIOSH) 2002 review – Health effects of occupational exposure to respirable crystalline silica



Background: Chest radiographs are an easy and relatively inexpensive method for imaging the tissues and structure of the thorax (chest). Chest x-rays are typically taken with two views, a frontal (posterior-anterior or PA), and a lateral view. Additionally, oblique views, angle from either side, are sometimes added to assist the reader. Chest radiographs are a useful tool in diagnosing pneumoconioses or dust diseases of the lungs.

The International Labour Office (“ILO”) is the International Labour Organization’s research body and publishing house. Since 1950, the ILO has periodically published Guidelines on how to classify chest x-rays for pneumoconioses. The most recent edition (2000) of the Guidelines, replaced the 1980 revised edition. The ILO Classification helps describe and record x-ray abnormalities of pneumoconioses in a simple, systematic, and reproducible manner, for epidemiological studies, screening and surveillance, clinical purposes, medical research, and aiding international comparisons of data.

“B” Reader Program: In 1974, after studies of surveillance programs for coal miners revealed unacceptable degrees of variation amongst x-ray readers, the National Institute for Occupational Safety and Health (NIOSH), in conjunction with the ILO, began the “B” reader program (so named because of the Black lung or Coal Workers’ X-ray Surveillance Program), with the intent to train and certify physicians in the ILO Classification system. The “B” reader certification examinationwent into full operation in 1978. NIOSH “B” reader approval is granted to physicians with a valid medical license who demonstrate proficiency in the classification of chest radiographs for the pneumoconioses using the ILO classification system. After passing the B-reader proficiency examination, a B-reader qualification by NIOSH designates physicians as competent in classifying pneumoconiosis films. I am a NIOSH-certified “B” reader, and have been so since 2003.

ILO Classification: The ILO Classification allows for systematic recording of the radiographic findings for all types of pneumoconioses. The Classification is designed for reporting the findings on a posterior-anterior view of the chest, but this does not exclude the use of other views in the clinical assessment of the patient. The x-ray should be analog-type (not digital) and of standard size (no less than 14 x 17″).

The ILO Classification system includes printed Guidelines and standard x-rays. The reader compares the subject chest x-ray with those of the standard set. The standard films provide differing types (“shape and size”) and severity (“profusion”) of abnormalities seen in persons with pneumoconiosis, including asbestosis, silicosis, and coal-workers’ pneumoconiosis. The reader then classifies the subject film, often recording the findings on the NIOSH Roentgenographic Interpretation form (sometimes referred to as the ILO form). The ILO Classification system pertains to pulmonary parenchymal (tissue) abnormalities (small and large opacities), pleural changes (pleural plaques, calcification, and diffuse pleural thickening) and other features associated, or sometimes confused, with occupational lung disease.

Quality of x-ray: Even when an obvious radiographic abnormality is present, it is necessary to review the chest x-ray in a systematic fashion. The ILO evaluation begins with an assessment of the x-ray quality. There are four grades of radiographic quality in the ILO system. Quality 1 is a good quality film, quality 2 and 3 are acceptable but with some technical defect, and quality 4 is unacceptable for ILO classification. The degree and location of film quality defects or artifacts determines the overall quality rating. Technical defects should be taken into consideration by the reader. A common quality defect, under-exposure, results in a tendency to read more profusion than would be recognized on an optimally produced radiograph. In other words, a reader is more likely to see mildly increased interstitial changes even though they are not present. Conversely, over-exposure produces the opposite affect.

Small parenchymal abnormalities: After assessing the x-ray quality, the B-reader evaluates the x-ray for the presence of any small parenchymal opacities consistent with pneumoconiosis. He or she will compare the subject PA radiograph with the ILO standard films to arrive at the profusion, shape/size, and location of small opacities.

  1. Profusion: Profusion refers to the concentration of small opacities in the affected zones of the lung. Using the Standard x-rays, the profusion (concentration) of small opacities is classified on a 4-point major category scale (0, 1, 2, or 3), with each major category divided into three, giving 12 ordered subcategories of increasing profusion: 0/-, 0/0, 0/1, 1/0, 1/1, 1/2, 2/1, 2/2, 2/3, 3/2, 3/3, and 3/+. Category 0 refers to the absence of small opacity and category 3 represents the most profuse. The major category (first number) represents the profusion felt to best fit the subject film, and the minor category (second number) represents the profusion seriously considered as an alternative. According to the American Thoracic Society (ATS), profusion 0/1 and 1/0 is the dividing point generally taken to separate films that are considered “negative” from those that are considered to be “positive.”
  2. Shape/size: The small parenchymal opacities are either rounded or irregular (linear). The small, rounded opacities are “p” (up to about 1.5 mm), “q” (about 1.5 mm to about 3 mm), or “r” (exceeding about 3mm and up to about 10 mm). Small, irregular opacities are classified by width as “s“, “t”, or “u” (same respective sizes as for small, rounded opacities.
  3. Location: Each lung is mentally subdivided by the reader into 3 evenly spaced zones: upper, middle, and lower. The zones in which the small parenchymal opacities appear are recorded.

Large opacities: A large opacity is defined as any opacity greater than 1 cm in diameter. They are classified as Category A (for one or more large opacities whose combined longest dimension does not exceed about 50 mm), Category B (for one or more large opacities whose combined longest dimension exceeds 50 mm but does not exceed the equivalent area of the right upper lung zone), or Category C (for one or more large opacities whose combined longest dimension exceed the equivalent area of the right upper lung zone).

Pleural abnormalities: Pleural abnormalities are reported with respect to type (pleural plaques or diffuse pleural thickening), location (chest wall, diaphragm, or other), presence of calcification, width (only of in profile pleural thickening seen along the chest wall edge), and extent (combined distance for involved chest wall).

Other abnormalities: There are 29 “obligatory” symbols representing important features related to dust diseases of the lungs and other etiologies. These symbols are: aa atherosclerotic aorta; at significant apical pleural thickening; ax coalescence of small opacities; bu bulla(e); ca cancer; cg calcified granuloma or lymph node; cn calcification of small pneumoconiotic opacities; co abnormal cardiac shape or size; cp cor pulmonale; cv cavity; di marked distortion of an intrathoracic structure; ef pleural effusion; em emphysema; es eggshell calcification; fr rib fractures; hi enlargement of non-calcified hilar nodes; ho honeycombing; id ill-defined diaphragm border; ih ill-defined heart border; kl septal (Kerley) lines; me mesothelioma; pa plate atelectasis; pb parenchymal bands; pi pleural thickening of an interlobar fissure; px pneumothorax; ra rounded atelectasis; rp rheumatoid pneumoconiosis; tb tuberculosis; and od other disease or significant abnormality. Finally, the reader comments on any other abnormal features of the chest radiograph or other relevant information.

ILO “B”-readings are required for OSHA silica screening and surveillance compliance.

To learn more, click here. 

For a current list of “B”-readers, click here.

OSHA Required Silica Surveillance

OSHA’s new crystalline silica standards require medical surveillance (silica screening) of employees working with and around crystalline silica within 30 days of employment and at least every 3 years afterward.

These exams must be performed by a duly licensed health care professional, and must include:

1) Medical and work history that focuses on past, present, and anticipated exposure to respirable crystalline silica, other occupational dusts, respiratory system history, smoking history, and history of tuberculosis

2) Physical exam focusing on the respiratory system

3) Chest x-ray with ILO “B”-reading by a NIOSH-cerified  “B”-reader

4) Spirometry test by NIOSH-certified technician


5) Test for latent tuberculosis

We offer all of these services in a one-stop location in Houston, Texas for your employee surveillance program. We can help you meet your compliance needs in a simple, sane fashion.