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Occupational Asthma
Lead-Free Solder
Solvents Overview

Hazardous smoke and fumes, harmful to your health if inhaled, are present in many workplace environments. Operations using lead-free solder, lasers, solvents, and glues are especially at risk. Overexposure can lead to serious – and possibly long term – medical problems.

Health difficulties such as nosebleed, eye irritation, and sore throat are occurring with increasing frequency in the workplace, as are incidences of dermatitis, occupational asthma, and, in some cases, permanent lung damage.


“Occupational Asthma is a disease characterized by variable air flow limitation and/or airway hyper-responsiveness due to causes and conditions attributable to a particular occupational environment and not to stimuli encountered outside the workplace.” (Bernstein et al 1993)

Fumes and gases in industrial areas are often dangerous to the people working in those areas. Some of these substances are readily visible or have a distinct odor; others are invisible and odorless. Many are toxic and can lead to allergic reactions, sometimes progressing to occupational asthma.

Occupational asthma is a major issue in electronics manufacturing because when a worker develops occupational asthma, they must be removed from the working area, sometimes permanently. In some countries, cases of occupational asthma due to flux fumes and/or isocyanates have already lead to legal claims against employers.

Occupational asthma is often indicated by symptoms common to 'hay fever' – an itchy, blocked, or runny nose, often accompanied by sneezing and glazed, itchy, or watering eyes.

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The transition to lead-free soldering has reduced strain on the environment, but for the operator, the hand soldering process has become more dangerous. The lead in the solder is gone, but to get the solder wire to flow properly, substantially more flux must be used. 

The temperature needed to create a good solder joint using lead-free solder is also higher, causing a stronger reaction within the flux and creating more solder smoke with a greater number of particles. Lead-free soldering produces up to 250 % more particles between 0.5 and 1.0 microns in diameter, the size that is the most dangerous to inhale. In addition to particles, solder smoke can contain isocyanates, aldehydes, and other unhealthy substances.

Lead-free soldering causes up to 250 % more particles in the breathing zone … roughly 20 million particles between 0.3 and 1.0 microns in diameter per cubic foot, or about 700 million particles per cubic meter.

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How particles of different size get caught in different parts of the human respiratory system:

Health problems that are related to particles and gases in the electronics industry:

- Early indication, very common in the electronics industry.

Respiratory problems
- Worsening of existing asthmatic conditions
- Occupational Asthma
- Irritation of the eyes and upper respiratory tract

Early symptoms are:
    * Watery eyes
    * Runny or blocked nose
    * Sore throat
    * Coughing
    * Wheezing or breathing difficulties


The following shows exactly what an operator could possibly breathe in during 90 minutes of lead-free soldering.

Standard lead-free 3% type ROL1 no-clean flux solder wire was melted continuously with a standard iron. The suction nozzle of a high efficiency fume extraction system was positioned near the tip of the iron. Just 90 minutes later, a nozzle-mounted net had captured a substantial amount of particulates.


This test distinctly shows the importance of using a fume extraction system, even when soldering only once in a while or for just a few hours a day. The captured particles are primarily condensed residues from flux. Without a filter system these particles will be partly inhaled by the operator with the remainder spread over the work object and workplace. In contrast, a proper filter system will eliminate not only the particles, but will also catch and eliminate dangerous gases created in the soldering process.

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Industrial lasers can also generate harmful fumes when used on different types of materials in the manufacturing process. These fumes are known collectively as Laser Generated Air Contaminants (LGACs).

LGACs fall into two categories: particles and gases

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  • Respirable particles – Many particulate LGACs are very small (generally less than 1 micron in diameter), so     they can be easily inhaled.
  • Toxic particles – Some particulate LGACs may cause allergic, carcinogenic or toxic effects, such as the     chrome and nickel particles produced when working with lasers on stainless steel.
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  • Volatile Organic Compounds (VOCs) are often produced when working with lasers on plastics.
  • Many VOCs already have Workplace Exposure Limits in place according to COSHH (control of substances    hazardous to health).
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Workers exposed to organic solvents for an extended time period incur increased risk of the following health issues:

  • Chronic damage to the nervous system, which can result in concentration and memory impairment, personality    changes, and permanent tiredness.
  • Reduced sensitivity to touch
  • Restless arm/leg syndrome
  • Skin dryness and irritation; non-allergic eczema
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Few workers understand the risks of exposure to solvents, yet many are exposed to them on a daily basis. Everyone working in an industrial environment comes into contact with chemicals that contain solvents. How dangerous the chemicals containing the solvents are depends on the properties of the substances and the precautions taken when handling them.

Organic solvents are absorbed primarily through the mucous membranes (total area: 80-200 m²), but some can also be absorbed through the skin (total area approximately 2 m²) or digestive system (total area approximately 10 m²).

There is a noticeable trend of people becoming more sensitive to allergic materials, such as airborne particles and solvents, in industrialized societies. This indicates a need for improved extraction equipment and precautions.


Isocyanates Isocyanates is the name of a large family of substances such as TDI (toluene-2,4-diisocyanate), MDI (diphenyl-methane diisocyanate), and HDI (hexa-methylene diisocyanate) used extensively in industrial workplaces. There are a large number of different isocyanates with different characteristics, but common to all of them is that they cause health problems, especially when inhaled. One of the largest areas of use for isocyanates is in the manufacture of polyurethane plastics (PUR). PUR appears as a soft compact foam and is found in coatings and other chemical products. Approximately 5 % of all plastics used are currently PUR and its usage is increasing. However, during the polymerizing and heating of PUR, a number of isocyanate combinations are formed. When heating phenyl formaldehyde resin, methyl isocyanates are formed.

Isocyanates can easily be absorbed through the skin and through the mucous membranes. In contact with water they form amines that will stay in the blood for a long time. Isocyanates are also found in polyurethane materials (coatings), glues, and varnishes.

Isocyanates cause health hazards – especially when inhaled in the form of gas, steam, dust, or aerosol droplets. Inhalation can cause irritation in eyes, mucous membranes, and respiratory system with symptoms resembling asthma or bronchitis and decreased lung function. The risk of hypersensitivity is high.

Isocyanates can also cause skin irritation. Repeated contact can cause eczema, and in some cases, skin allergy. Isocyanates have a very low limit value … so low that you may be exposed to dangerous concentrations without noticing, as isocyanates are invisible and odorless at low levels. An allergic person can develop problems even when exposed to concentrations below the hygienic limit value.

Recently, new health hazards have been discovered with certain PUR coatings and some PUR glues used in the manufacture and repair of printed circuit boards. The same risks occur when working with coated optical cables that contain small amounts of PUR and coated wire. When these materials are heated, isocyanates are formed in such high concentrates that it can cause asthma. It is believed that the thermal segregation starts at 150-200°C. There are also strong reasons to suspect that isocyanates can be formed when heating resin products like fluxing materials.

Alcohols Inhalation or skin contact with alcohols such as methanol, ethanol, or isopropanol can cause dizziness, headache, disturbed vision, or fainting. Absorption over a longer period can permanently damage the eyesight of the victim.

Aldehydes Aldehyde solvents such as formaldehyde and acetaldehyde are transformed when heat is applied to them, resulting in fumes that have an irritating effect on the eyes and respiratory organs. Inhalation can induce headache, dizziness, and fainting in severe cases.

Esters (acetates) Esters such as ethyl acetate and dioctyl phthalate are often used as solvents and dissolvents in the manufacture of paints, plastics, and synthetic fibers. Like most solvents, they cause irritation of the respiratory passages, but long term exposure causes kidney and liver damage.

There are many other solvents in common use, including ketones, mercaptans, organic acids, and ethers, all of which have an effect on the human body, primarily on the respiratory system. Skin contact (splashes) resulting in eczema is a secondary, but fairly common occurrence.


Why are solvents dangerous?
Can the body break down solvents?
Are all solvents equally dangerous?
What parts of the body do solvents harm?
Is the damage done by solvents permanent?

Q:Why are solvents dangerous?

A: Solvents dissolve fat. The easier they dissolve fat, the easier they are absorbed by the body and the greater their capacity for doing damage. The ability to dissolve fat is partly the reason why solvents are used, and is one of the main reasons why they are so dangerous if they get into your body.
The cells of the brain contain a high degree of fat. Since the brain works like a sponge in absorbing solvents, this puts the nervous system at great risk.

Q:Can the body break down solvents?

A:Yes, the liver can break down many of the solvents. But unfortunately, the chemicals formed when these substances are broken down can be even more dangerous than the original solvents.
It can take a long time for your body to break down solvents – so long, in fact, that the body cannot get rid of everything during the night or even over the weekend. This is very serious because it means that solvents can accumulate in your body, sometimes causing irreversible damage.

Q:Are all solvents equally dangerous?

A: No, some are safer than others. Also, the body absorbs some more slowly than others. If you have a choice of solvents, use one that causes as little harm as possible and is absorbed very slowly.

Q:What parts of the body do solvents harm?

A:That depends on the solvent in question. The brain, bone marrow, liver, and kidneys are susceptible to damage, but the most common effect is damage to the nervous system. Just as with alcohol (which is a solvent) as the body absorbs more and more of a solvent, reactions become slower and judgment is impaired. In many jobs, those events can open the victim to other, even more extreme dangers.

Q: Is the damage done by solvents permanent?

A: Unfortunately, in many cases the damage is irreversible. It has been proven that occupational symptoms appear slowly over a long period. By the time a condition is diagnosed, lasting damage may have been caused to the nervous system, respiratory system, eyes, brain, liver, and kidneys.

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The main health risks of long-term exposure to glues are:

- Skin irritation
- Skin drying
- Allergic contact eczema
- Asthmatic problems from inhalation of glue dusts and solvents

The level of health risk varies depending on the type of glue being used, with non-hardening glues (“hot glues” that gain strength by cooling) being least dangerous. Glues that strengthen by drying are somewhat more harmful, with water‑based glues being less dangerous than solvent‑based types. Glues that pose the highest risk of health concerns are “hardening” glues that cure independent of surrounding conditions.

Polyurethane glues – Polyurethane glues contain isocyanates that are released during application. Isocyanates can cause:

  • Asthma
  • Hyper-sensitivity to isocyanates
  • Breathing problems when exposed to other fumes (perfumes, motor vehicle exhaust, tobacco smoke, etc.)
  • Irritation of skin and eyes
  • Reduced lung capacity

Acrylate glues – Acrylate glues contain high concentrations of acrylate, methacrylate or cyanoacrylate esters that can cause contact allergies.

Epoxy glues – Epoxies can cause:

  • Skin irritation
  • Allergic contact eczema

Silicone glues – Residue products of silicone glues include oximes, alcohols (alcoxy “methanol”, methoxy), and acetone. These volatile by-products can cause:

  • Cancer
  • Skin allergies
  • Serious eye damage on contact

Acetone glues – Acetone glues can cause:

  • Eye irritation
  • Dry skin
  • Blisters
  • Tiredness (from fume inhalation)

Methanol glues – Methanol glues are very hazardous, even with minimal exposure. They can cause poisoning through contact, ingestion, or fume inhalation.


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