Commercial printing: when every solvent passes and the air still fails

A pressroom is the clearest example in industry of one problem: every individual solvent result can come back under its limit, and the air can still be out of compliance.

The mixture rule that gets skipped

OSHA has a rule for mixtures. When two or more hazardous substances act on the same organ system of the body, their combined effect is what counts. To check it, divide the airborne concentration of each substance by its own limit and add up the results. That sum must not be more than 1.

A pressroom typically has the following in the air:

• Toluene, with a permissible exposure limit (PEL) of 200 parts per million (ppm)
• Methyl ethyl ketone (MEK), 200 ppm
• Isopropanol, 400 ppm
• Ethyl acetate, 400 ppm
• A heptane or naphtha fraction
• A glycol ether or two in the fountain solution

Suppose five of those each sit at 35 to 40% of their own limits. The sum comes out near 2, so every line on the report reads "below the PEL" while the air is out of compliance by a factor of two.

This changes how you should buy the survey. A "total hydrocarbons" or "total VOC" number cannot be used in the mixture calculation. (VOC stands for volatile organic compounds.) You need a separate result for each solvent by name, so the laboratory has to be told in advance which chemicals to measure. Someone also has to read the safety data sheets for the blanket wash, fountain solution, ink and pressroom cleaner, and that has to happen before the visit, not after.

→ Solvent vapor air monitoring · Air monitoring surveys

Where the solvent exposure actually occurs

It is not while the press is running. Washup is when solvent exposure is highest. That covers blanket and roller wash, whether applied by hand or by an automatic system, along with the rags and the open container the rags go into. Heatset web dryers move solvent out of the room but concentrate it in a stack, and that stack is usually the reason you hold an air permit, and possibly an oxidizer.

Fountain solution is the quiet contributor. Alcohol substitutes and glycol ethers evaporate all shift long from a large open surface, adding a low, steady background concentration that pushes the mixture sum up without ever producing a peak anyone notices. One glycol ether, 2-butoxyethanol, carries a skin notation, meaning it can be absorbed through the skin. Skin contact matters, and the air sample will not capture it.

"Printer's asthma" is not one disease

The phrase comes from older occupational medicine literature, where it described asthma among press and bindery workers. The useful way to read it today is that it never had a single cause. The possible causes found in print shops include:

• Gum arabic in fountain solutions
• Acrylate monomers in UV-cure systems
• Isocyanates in laminating adhesives
• Enzyme and dye dusts in specialty work

They behave differently and need different controls, so the old label is worth knowing about but not worth using as a diagnosis.

UV-cure inks: air monitoring is the wrong tool

This is the part where the honest answer costs us a sale.

Inks cured by ultraviolet light (UV) or electron beam (EB) are built on acrylate monomers and oligomers. Common ones are hexanediol diacrylate (HDDA), tripropylene glycol diacrylate (TPGDA), trimethylolpropane triacrylate (TMPTA) and their relatives. Most have no OSHA PEL and no threshold limit value (TLV) from ACGIH. They do not evaporate readily, but they are potent skin sensitizers, meaning they cause skin allergy, and workers are exposed by touching uncured ink.

The risk is therefore at washup, at plate and blanket handling, at ink-key adjustment and anywhere someone touches wet ink. Air sampling will come back "none detected" from a room with a real skin rash problem. What helps is:

• Selecting glove material that has permeation test data showing how fast acrylates pass through it
• Taking surface wipe samples to map where uncured ink is actually being spread
• Ending the habit of washing hands with solvent, which strips the oils from skin and lets more chemical in

Glove selection and wipe sampling are outside the four fields we work in.

Isocyanates in lamination

Solvent-free, two-part polyurethane laminating adhesives for flexible packaging contain aromatic isocyanates, including methylene bisphenyl isocyanate (MDI). OSHA's limit for MDI is a 0.02 ppm ceiling limit, a level that must not be exceeded at any time. ACGIH's TLV is 0.005 ppm as a time-weighted average (TWA). Exposure is highest at adhesive mixing and pouring, at the coating head and during machine cleanup, not during the run.

The sample must be collected on derivatizing media, which is a specially treated filter. Ordinary charcoal tubes return nothing useful.

→ Isocyanate air sampling

Noise and paper dust

Pressrooms are noisy, but the sources most worth a survey are usually in bindery and finishing: folders, stitchers, guillotines and inserters. Their noise comes in sharp bursts, not as a steady sound. Add to that compressed-air blow-off on sheet feeders and delivery.

Compressed-air noise is high-frequency, and it can often be fixed with an engineered nozzle for a few hundred dollars. You can only make that call, however, from an octave band analysis, which breaks the noise down by frequency from low to high. An overall decibel (dBA) reading will not tell you.

Paper dust from sheeting, trimming and bindery has no limit of its own. It falls under OSHA's catch-all category for general dust, Particulates Not Otherwise Regulated, where the limits are 15 milligrams per cubic meter of air (mg/m³) for total dust and 5 mg/m³ for respirable dust. Remember that coated stock is not only cellulose, because clay and carbonate fillers make it a mineral dust as well.

→ Noise surveys · Dust air monitoring

The Form R threshold that is lower than you think

Form R is the annual Toxics Release Inventory (TRI) report filed with EPA. Toluene, methanol, glycol ethers and several pigments are on the TRI chemical list, and commercial printing is one of the industries the program covers.

Inks, washes and fountain solutions count as "otherwise used", not as manufactured or processed, which puts the reporting threshold at 10,000 pounds per year, not 25,000. Some printers ran their numbers against the higher figure and have been under-reporting for years without knowing it.

→ Form R and Toxics Release Inventory (TRI) reporting