175 watt mv tube is 95% blackened and hard to light do these have a high risk of explosion?

Nope, no risk at all. Unless you shake it while it's on.

Nope, no risk at all. Unless you shake it while it's on.

Ok cool good to know! Thanks

The internal pressure inside a MV lamp, is significantly lower than in a MH lamp. Add the fact that the mercury isn't corrosive toward the quartz, and that the arctube in MV lamp, burns colder than in a MH lamp..

Any lamp of any type can explode at some point if there is a defect in the envelope, or for discharge lamps, as result of ballast failure. The odds are low enough that the lamp can be considered safe as long as you don't do stupid things with it

The violent explosion risk of MV (and HPS) comes mainly (and virtually only) from a ballast failure or mains overvoltage failure (both leading to a severe lamp overpower scenario). Because you can never rule these failure out, you have to design the fixture to contain the explosion with all high pressure lamps (HIDs, halogens,...; or use lamps featuring internal additional containment structures, so open fixture rated), not only for the MHs.
But only the MH (mainly the quartz ones) are known to be prone to explode because of lamp internal effects alone (thermal runaway at the EOL,...), so are known to explode even on a perfectly fine ballast and correct feed.

How did you get sunburned from the metal halides? I thought the outer envelope is supposed to block UV...

I have heard of people getting sunburned in a gym from MH lamps.

I have heard of people getting sunburned in a gym from MH lamps.

I have heard of that too but it only happens when the outer envelope gets busted.

How did you get sunburned from the metal halides? I thought the outer envelope is supposed to block UV...

It does not block it completely, but it reduces it to a level considered safe with normal use.
And normal use means lamps being few meters away from people, high in the fixtures. Not few cm away, when you are handling them powered ON while servicing the fixtures.
At that short distance the UV intensity could be still above safe limits, but no one is supposed to be such close to them without knowing what he is doing there and without proper PPE (the explosion is there the main risk, but usually the protection against it usually protects against the UV too).

The exposure time when maintaining the lighting is very short, and you don't change lamps all day every day. How does that sum up to any significant exposure ?

Sometime in the early 1970’s there was an article in the Long Island Star Journal about many people who had attended a high school basketball game having  suffered eye damage. It was traced to a cracked 1000 watt mercury vapor bulb
in one of the high bay fixtures in the gym. I had remembered reading the Duro Test annual report saying that they had developed a safety mercury lamp( they may have been the first) that would extinguish if the outer envelope was damaged. I sent a copy of the article to the president of Duro Test. Several weeks later, I received a nice thank you letter, saying that they had sent a salesman to the school and that the school district had purchased over a hundred of the 1000 watt safety mercury lamps.

Sometime in the early 1970’s there was an article in the Long Island Star Journal about many people who had attended a high school basketball game having  suffered eye damage. It was traced to a cracked 1000 watt mercury vapor bulb
in one of the high bay fixtures in the gym. I had remembered reading the Duro Test annual report saying that they had developed a safety mercury lamp( they may have been the first) that would extinguish if the outer envelope was damaged. I sent a copy of the article to the president of Duro Test. Several weeks later, I received a nice thank you letter, saying that they had sent a salesman to the school and that the school district had purchased over a hundred of the 1000 watt safety mercury lamps.

Of course, a broken lamp, with full UV blast from its arctube, is very severe danger even from a distance, but the point was about the possibility of a good, intact lamps to cause sunburns...