SAMPLING METHODS

TRAINEE OBJECTIVES

After completing Section 7, you will be able to:

1. List the limitations of certain sampling methods, such as visual exams, past records, and quick-check chemical methods.
   
   
2. Describe the following sampling methods, X-ray Fluorescence (XRF), paint chip analysis, and air sampling.
   
   
3. Describe why precautions are necessary if prior identifications are not done.
   
   
4. Describe what precautions will be needed in most cases where any lead is found.

INTRODUCTION

Now that the very real hazards posed by lead have been described, let's begin the process of controlling the hazard. We know that lead paints were widely used in the past. What is the likelihood that a given structural steel dismantling job will involve lead paint-coated metal? There are no published statistics on the question. The likelihood is high. The best policy is to assume that all jobs involve lead unless proven otherwise. However, experience from asbestos projects indicates that while assuming the presence of a toxic substance is prudent for workers, there is a tendency to ease up on precautions without real test results. Because of this tendency, it is recommended that surfaces be tested for lead, preferably before the job begins.

Testing is not as difficult to obtain as you might think. First of all, much dismantling work is done on publicly owned structures, such as bridges and elevated roadways. Because of the problem of childhood lead poisoning, most cities and states have some capability for lead surface testing.

Secondly, the asbestos problem has made local governments and facility owners much more aware of their legal obligations to disclose information about foreseeable hazards on a renovation or demolition job.

Thirdly, there are environmental considerations. In one Massachusetts case, a bridge renovation job caused lead poisoning in children living in homes adjacent to the approach of the bridge. Eventually a layer of contaminated topsoil had to be removed from numerous yards. In a Maryland bridge case, a contractor was fined for polluting a waterway due to the lead from torch cutting falling into the river below.

In summary, the contractor is clearly justified in requesting test data on lead prior to bidding on the job. After all, lead precautions do add to the cost of the job. It is likely that facility owners will increasingly do this testing on their own, and will write lead hazard specifications right into the bid documents. They will do this to protect themselves from liability. In the meantime, union leaders and contractors should insist that tests be done prior to a job or as early as possible.

SAMPLING METHODS

While it is not expected that Laborers will be routinely involved with identifying lead on these jobs, it is important to have a general understanding of the methods available. In some cases, local union officials and/or contractors may need to arrange for such testing. Methods are described below.

Visual Methods

While lead paints are associated with given colors, such as red and battleship gray, there are many other pigments which can give these colors. As a result, lead cannot be identified by color or other appearance. This is not an acceptable method for identification.

Past Records

Past purchase or safety records may identify the use of lead paints. If the records are specific enough to link the paints to the building or structure in question, then this may provide an acceptable method. But keep in mind that it is doubtful that adequate records will be available. Either the lead content of the paint might be missing or the precise identification of where the paint was used might not be available. Past records must be used carefully: if there is uncertainty then further testing must be done.

Quick-Check Chemical Methods

Chemical methods are available and they are sometimes advertised in trade journals. They typically use the chemical sodium sulfide for detection of lead-based paint. These methods work by turning the chemical gray or black in the presence of lead. While the convenience, simplicity, and speed of this test are appealing, it is not reliable enough to qualify as an adequate test. Among the drawbacks of this test are:

• It only gives an estimate, as it does not provide the concentration of lead in the paint to be determined.
  
  
• The color change is difficult to determine for dark colors.
  
  
• The presence of other common metals, such as iron or copper, can cause a similar color change.
  
  
• The solution deteriorates quickly which can give misleading results.

In sum, this method sometimes works, but sometimes it does not. It is not a reliable test and should not be used.

XRF-Analysis

There is a portable instrument which can identify the concentration of lead on the spot. It is called the XRF analyzer (Figure 7-1), which stands for X-Ray Fluorescence. This instrument contains a carefully enclosed tiny radiation source-a small speck of radioactive Cobalt 57. The instrument is held flush against the painted surface to be tested. It then releases a small amount of radiation, which excites any lead atoms in the paint. As they return to a stable state, the lead atoms give off characteristic x-rays.

The instrument detects the x-rays, converts their strength to an electrical signal, which is then counted. The more lead that is present, the higher the reading. The XRF analyzer gives readings in "mg/cm²," or milligrams of lead per square centimeter of surface. One mg/cm² is considered the action level for lead precautions. This level has been set because it is the lowest level which can be reliably detected. This level is likely to be lowered in the future as instruments are improved.

The XRF analyzer is valuable because it allows a speedy determination of whether lead is present. It is widely used by city health departments to check lead paint problems in housing and apartments. However, the instrument must be used carefully, and it requires a training program all its own. Because it uses radiation, technicians can be exposed if not careful. XRF units do have shielding, but technicians typically wear radiation badges as a back-up to detect any radiation exposure. Furthermore, the device must be used carefully to avoid misleading results. In many states, XRF analyzer technicians must be licensed.

Paint Chip Analysis at a Lab

Paint chip analysis is also done, and commonly used to double check low XRF analyzer readings (at the lower limit of detection). It is important that the paint chip be "representative" of the coating in question and should include all paint layers (not just the top). It should not include bits of the base metal or rust. Results are based on total weight of the paint sample and the weight of the base metal or rust could give a false result for lead content. The proper procedures for sampling must be followed. These procedures are as follows:

• Each sample must be sealed in a separate bag, with its own sample number.
  
  
• The identification of sampling locations for each sample must be identified with sample date and name of person removing the sample with that person's signature.

A paint sample is usually taken by using a sharp knife and cutting a piece at least one inch square. It's then put in a plastic zip lock bag or glass bottle and labeled as to location. It is then shipped to a nearby lab where it is analyzed by approved analytical methods, such as atomic absorption, computer-enhanced x-ray fluorescence, or atomic emission spectroscopy.

For asbestos, the analytical methods used for air sampling do not provide sufficient accuracy to allow identification of asbestos. Because of this, only bulk tests of material can be used for identification purposes. However, for lead, the analytical procedures used in air sampling methods are sufficiently accurate to identify the presence of lead. This means that air sampling can be used to indirectly identify lead.

Air-Sampling Methods

Air samples are taken by outfitting a worker with an air sampling pump that is worn on the belt. A small mounted filter is clipped to the collar of the worker so that it is in his breathing zone. The filter is connected to the pump by a small length of hose. The pump draws in air across the filter, and the lead fumes or dust gets trapped on the filter. At the end of the shift or job, the filter is sent to a lab for analysis. A positive finding indicates that lead is present. Air sample exposure criteria are described in Section Three. If this method is used, it is important that it be done while typical hot work is going on. A sample taken in quiet conditions may not reveal any lead in the air, and it could lead to erroneous conclusions about the potential hazard to workers.

INTERPRETATION OF RESULTS

There are no hard and fast rules for evaluating lead identification data. If lead is found to be present in chips or air, some precautions will be needed. Chip analysis results listed in percentage are more readily understandable, and should be requested. Studies of dismantling projects have found chip results ranging from 6% to 90% lead content. Some surface results may be in milligrams of lead per square centimeter. This is harder to interpret, and labs should be able to convert it to a percentage. Remember also that the thickness of the coating can be a factor. A thick coating of 10% lead may cause higher exposures than a thin film of 40% lead. This is why air sampling is ultimately also important. It can provide a better picture of the hazard presented to workers by the interplay of the amount of lead present, the environmental conditions involved and the fumes and dust potential of the work procedures.