Group Checks, Success with a Cost, and Skill Challenges
These three concepts are meant to be used in tandem, but can be cherry picked to suit your style of play. I have the most experience using them together.
This is pretty simple. Half the group has to pass at doing some thing. In the examples you provided, this represents the party collectively crossing the rickety bridge, or a group effort to handle Materia.
Perhaps the Bare Minimum of 2 out of 4 people make the check/save.
"Wizardface nearly falls through a gap in the rickety bridge, but McFighterson manages to grab his wrist in time. The rest of the walk is slower as you take your time, but there are no other events of note."
You can secretly game this by knowing how likely it is for at least half the party to pass, based on the dc and their bonuses, and you don't have to worry about the wizard with the -1 acrobatics (or whatever).
If your group is bad at remembering inspiration, this is a good time, in my opinion, to remind them it exists.
Success with a Cost
"SwaC" is a hugely useful tool (okay, no one calls it that... yet). Maybe you want to leverage inspiration, mundane gear, spell slots, or hp.
Wizardface starts to slip through one of the tiles. McFighterson and La' Rouge are close enough to help, but they'd have to sacrifice the --insert thing here-- to get to him in time. Maybe it's not so bad at the bottom? What do you do.
This can be preemptively used, without rolling. I've had situations where I allow things to happen, wherein the party pays up front (usually at the party's suggestion).
Party: If we spend 2 inspiration, can we assume that the party makes it across?
DM: Of course. That sounds reasonable. Please describe your crossing and a hardship that you overcame
This allows them to enjoy the narrative feel where there is still a cost.
Disclaimer: I have adopted this from Matt Colville and his video on Skill Challenges.
This does not work for every scenario, but can be made to work for many. Choose a threshold, based on difficulty of the thing. Maybe it's 3 successes and 3 failures (adjust the number of successes for more difficult things). It may help you to think of this as a "race against time". In the case of the Materia example:
Barry Barbarian knocks over a box of the unstable element and one of the canisters begins to hiss and glow. You guys don't have long before it ignites and sets off the nearby canisters. The goal is three successes before three failures.
Then the group goes around, requesting to make proficient skill checks. The same skill cannot be used more than once, by the same character. Characters must be proficient in the skills. Players should be able to justify the skill in question. "No, unless you can explain how animal handling would help, you can't use it."
This might go something like the following:
Barry Barbarian succeeds at a survival check to retrace their steps.
McFighterson suggests using athletics to pry open a door that had warped from the reacting Materia. Success!
Rapier la' Rouge attempts to find a shortcut using investigation, but is unable. A vent of plasma bursts from the rivets of a nearby wall, causing light burns.
Wizardface is trained in Arcana and thinks he can predict a reactive fissure in the nearby steel-work. Success!
The Party escapes, managing to salvage one container of the materia. A more careful extraction would have made them a fortune, but the group feels fortunate to have kept their lives.
Honorable Mention: Make failure less fatal
Is there something about your cool scenario that could save the failing character? Perhaps the ravine is sloped and leads off into some unseen area? Perhaps the highly reactive Materia irradiates (bestows a curse) onto the nearby characters? Maybe the collapsing building only does 6d6 damage instead of instant death?
This isn't always going to fit the tone you want, but often, you can find that the unknown is just as terrifying as the certainty of death.