Here's the MSDS for Trimethylbenzene. Not much to go on.

Appearance: colourless liquid
Melting point: -43.8 C
Boiling point: 169 C
Vapour density:
Vapour pressure:
Density (g cm-3): 0.876
Flash point: 48 C
Explosion limits:
Autoignition temperature:
Water solubility: slightly soluble

Doesn't seem TOO nasty,

R36 Irritating to eyes.
R37 Irritating to respiratory system.
R38 Irritating to skin.

More,

Stability
Stable. Incompatible with strong oxidizing agents. Flammable. May form explosive mixtures with air.
Toxicology
Typical STEL 35 ppm. Typical TWA 25 ppm. May be harmful by ingestion, inhalation or through skin contact. Skin, eye and respiratory irritant.
Toxicity data
(The meaning of any toxicological abbreviations which appear in this section is given here.)
ORL-RAT LD50 5000 mg kg-1
IPN-RAT LDLO 2000 mg kg-1
IHL-MUS 8147 ppm acute
IPN-GPG LDLO 1566 mg kg-1

Risk phrases
(The meaning of any risk phrases which appear in this section is given here.)
R36 R37 R38.


Transport information
Personal protection
Safety glasses, adequate ventilation.