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Bofa Americas, Inc. Market leaders in fume extraction and filtration.

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Bofa Americas, Inc. market leaders in fume extraction and filtration with unrivalled expertise in the development and production of the latest solutions for a wide variety of industries.

Lasing PVC.Advice and information.

Effects Of Fume

When PVC is burned during the lasering process the extremely corrosive, acidic Hydrogen Chloride or HCL is produced. It is imperative that this fume is removed quickly and efficiently for both the safety of the operators and to protect the laser and surrounding equipment.

Protecting Personnel

HCL is classed as a major health hazard, and as a result has a maximum exposure level of 1ppm (Part Per Million) over an 8 hour period. (from HSE EH40/2000 Occupational Exposure Limits).

Protecting The Laser

Not only is HCL a major hazard to health but it is also extremely corrosive. If this acidic fume is allowed to migrate onto the laser lens housing and associated components it will, over a period of time, cause irreversible corrosive damage.

Now we have established the problems that lasing with PVC can cause, we can look at how to extract the fume safely without damage to the extractor.

First of all it is imperative that all internal contact parts are lined in an acid resistant coating. The PVC upgrades available on the BOFA Advantage units have a specially developed 2 part epoxy for this purpose.

Next we come to filtration. The 2 stage pre filters used in the Advantage extractors are completely sealed. This is a very important factor as the fume that enters the pre filter chamber will drop in velocity separating the liquids into the sealed sump. Some extractors have absorbent pads to soak up this liquid. These pads rest directly under the pre filter bags that make it both very difficult and dangerous to handle on filter change.

Any of the HCL that passes through the 2 stage pre filter and HEPA filter will be absorbed within a layer of media that is specifically designed to absorb and neutralise the HCL gas.

Advantage units fitted with the PVC upgrade have an HCL sensor mounted within the exhaust of the system. This unit is specific to HCL and will only be activated when HCL is detected. Many extraction systems are fitted with gas detection sensors but these are normally for VOC (Volatile Organic Compounds) and will not be activated by HCL. It is advisable to check with the manufacturer of the extraction system to make sure an HCL sensor is fitted.

Health issues - Particulate

The particulate generated in most laser applications is sub micron in size and as such almost all is respirable. This gives rise to two separate concerns.

The quantity of dust being inhaled.

Dust of any kind can also become a substance hazardous to health under COSHH when it is present at concentrations in the air equal to or greater than 10 mg/m3 (as a time weighted average over an 8-hour period) of inhalable dust or 4 mg/m3 (as a time weighted average over an 8 hour period ) of respirable dust. Marking applications typically generate up to 1mg/s of fume and Cutting applications in excess of 10 mg/s.
The second is a reaction to the actual material of the particulate which may cause allergic, carcinogenic or toxic effects e.g. chrome and nickel compounds released from stainless steel are thought to be carcinogens.

Gases

Potential problems are usually associated with plastics which give off Volatile Organic Compound's when lasered, most of which have associated Occupational Exposure Limits (OEL). The table below covers a range of common plastics and lists the VOC's given off together with their OEL. PVC is worth a special mention in this context since it releases hydrogen chloride and small amounts of phosgene both of which are extremely toxic.

Laser efficiency

The optical system of the laser is susceptible to damage from particulate getting burnt onto the lens which reduces the laser efficiency and on marking applications can effect the quality of the code.

Additionally particulate in the laser beam can refract/reflect the light which diffuses the beam (see animation opposite).

Product contamination

Marking applications on open containers are vulnerable to particulate settling in the container which contaminates the product being filled.

These particles fall within the respirable range and need to be removed from the working environment to prevent bronchial or lung damage.

Table: Exposure limits

OEL (8hr) mg/m3
Benzene	9
1,3 Butadienne	22
Formaldehyde	2.5
Methylmethacrylate	208
Phenol	20
Creois	22
Toluene	191
Hydrogen chloride	2
Phosgene	0.08
Methylamine	13
THF(Tetrahydrofuran)	300