From Black Mesa: Wiki

(Temp text: The perils that Gordon Freeman finds along the game. For references, check here.)

Environmental Hazards

The Black Mesa Research Facility becomes a dangerous place after the accident, with pipes being broken, live wires falling, and chemicals being spilled. These are the hazards your HEV suit is programmed to recognize for your safety in any and all environs.

Acid or Corrosive Chemicals Coming into contact with Acid or other corrosive chemicals is very dangerous; the liquid will eat away at you and your HEV suit, killing you quickly.

Cold Exposure to extreme cold will sap the HEV suit's power, and prolonged exposure to low temperatures may be dangerous to your body as well.

Drowning Staying underwater until you run out of air will result in drowning. Health will drain until you resurface, then will slowly regenerate increments of 10 HP a second until all the HP lost from drowning has been regained.

Electrical Shock Exposure to live wires, electric fences, and other such hazards will electrocute you, injuring you and lowering your suit's power.

Heat Fire, steam, and other sources of extreme heat will burn you and damage your HEV suit's power levels.

Poisonous Biohazard Coming anywhere near a bio-hazardous liquid will start killing you slowly. If you need to go past a pool of it, do it quickly.

Radiation Radiation will slowly drain your health when you are exposed to it. Proximity to radiation will trigger the HEV suit's Geiger counter to warn of the danger.

Fall Falling from great heights can be very deadly, and the HEV suit does not protect from fall damage. Minor falls will do small amounts of damage, increasing in damage as the height fallen increases.

Explosives

In addition to the environmental hazards present, there are many explosive materials and objects in the facility that could kill you, or someone else, if you're not careful.

Explosive Barrel A barrel of volatile fuel. damaging it will cause it to ignite, if not explode; be warned, however, as the fire will eventually cause an explosion as well.

Propane Container A tank filled with propane. damaging it will cause it to ignite, and it will explode in a fireball shortly after.

Dynamite Crate A crate filled with Dynamite. Explosions, fire, or too many bullets will cause it's contents to detonate.

Land Mine A land mine planted by HECU forces. If you step on it, it will explode, but there are ways to detonate it from a safe distance...