Xylenes

>he has been using ...xylene...to take off old tape from the embrittled
>pages of comic books

Someone else will, I'm sure point out the enormous potential for damage
in a treatment of this sort, but I'll comment immediately on the safety
issue.  Xylenes (not 'xylene', because it is normally found as a mixture
of the ortho, para, and meta forms as well as a bit of ethyl benzene) is
a moderately toxic material and it is likely that your informant is not
using the material safely (the question itself suggests inexperience in
handling solvents). I'm tempted to post an MSDS (material safety data
sheet), but as they are quite difficult to interpret, I'll just show
some highlights.

Please note that I am *not* suggesting that Xylenes shouldn't be used by
people trained and equipped to handle it properly, but I do insist that
this material has no business in the amateur's toolkit (and I would make
the same assertion for most organic solvents).

The main hazard categories for Xylenes, as they are recorded in our
hazard reporting system (such systems vary widely from site to site and
the categories given here will not correspond to categories used at your
site) are:

  Hazards:  6 Flammables
           12 Slight Poisons
           15 Suspect carcinogen, mutagen, or reproductive hazard
           28 Skin irritant
           33 Hepatotoxin
           34 Nephrotoxin
           36 Blood and hemapoetic system toxin
           37 Lung irritant
           38 Eye irritant
           41 Skin-absorbable poison
           52 AB 1803 well monitoring chemicals
           53 SARA section 313 toxic chemicals
           54 Maximum contaminants levels list
           55 AB 2588 toxic hot spots A-II

According to an MSDS (this one comes from J.T. Baker) the Threshold
Limit Value (TLV/TWA) is 100 parts perm million, which is pretty low as
things go. I haven't done the calculations, but I think it would be
pretty easy to exceed this concentration in a non-lab setting ("adequate
ventilation" does *not* mean opening a window).  If someone is really
interested, let me know and I'll explain how to do the calculation.

Note that one of the routes of entry listed is skin contact so aprons
and (nitrile) gloves should be used.

Now, since someone is sure to ask, here are just a few (highly edited)
excerpts from an MSDS.  The part that should catch your eye is the
Chronic effects section.  Please consult a complete MSDS before using
this material.

    Health        -  2  Moderate
    Flammability  -  3  Severe (Flammable)
    Reactivity    -  0  None
    Contact       -  2  Moderate
    Hazard ratings are 0 to 4 (0 = NO HAZARD; 4 = EXTREME HAZARD).

    Laboratory Protective Equipment: Safety Glasses; Lab Coat; Vent Hood;
    Proper Gloves; Class B Extinguisher

    Threshold Limit Value (TLV/TWA):    (100 ppm)
    Short-Term Exposure Limit (STEL):   (150 ppm)
    Permissible Exposure Limit (PEL):   (100 ppm)

    Carcinogenicity:  NTP: No  IARC: No  Z LIST: No  OSHA REG: No

    Effects of Overexposure
      Inhalation and ingestion are harmful and may be fatal.

      Inhalation of vapors may cause headache, nausea, vomiting,
        dizziness, drowsiness, irritation of respiratory tract, and loss
        of consciousness.

      Inhalation of vapors may cause narcosis.

      Contact with skin or eyes may cause irritation.

      Ingestion may cause nausea, vomiting, headaches, dizziness,
          gastro-intestinal irritation, blurred vision, lowering of
          blood pressure.

      Chronic effects of overexposure may include kidney and/or liver damage.

    Target Organs
      Central Nervous System, Eyes, Skin, GI Tract, Blood, Liver and Kidneys

    Routes of Entry
      Ingestion, Inhalation, Skin Contact, Eye Contact, Absorption

                                  ***
                  Conservation DistList Instance 6:53
                 Distributed: Saturday, April 10, 1993
                        Message Id: cdl-6-53-014
                                  ***