According to theatrical legend, the shortest run in showbiz history was The Lady of Lyons in 1838. The curtain got stuck on the opening night, the audience went home and that was it.

I offer this historical titbit as comfort to the cast of God of Carnage, whose opening night on Tuesday was nearly ruined when a workman in a nearby side street severed power cables, plunging the theatre into darkness. At least they were in modern dress: I was once caught onstage during a power failure, and as the show was Mamma Mia! I had to grope my way into the wings in platform heels and a gold Lurex codpiece.

First nights are ghastly ordeals for actors. A recent study indicates that the stress endured is equivalent to being involved in a minor car crash, and that's without the intervention of the utilities. Everybody there is willing you to succeed or fail, and the only reaction from the darkness of the auditorium (or as the actor David Haig perfectly describes it, “the abyss”) is the forced laughter of friends and family or the equally deafening silence from critics and bitter rivals.

And if things are going to go wrong, they'll do so then, when everyone is shot through with adrenalin and the only expression is a collective rictus grin. Recent first-night gremlins have included a rogue sprinkler system drenching the stage before The History Boys, and a recalcitrant revolve at the Adelphi Theatre - ensuring that while Joseph may have had his dreamcoat, he had to manage without his troupe of Ishmaelites, who were supposed to ride on but were marooned in the wings.

Perhaps a hardhat and Day-Glo jacket should be the thesp's accepted attire, not doublet and hose. Walls descend without warning, doors jam and Cinderella's ponies pulling her golden carriage panic, defecate and bolt towards the orchestra pit.

No, what really matters is how the beleaguered actor deals with such crises. During a production of The Scarlet Pimpernel in which I appeared the guillotine that was meant to be severing the noblemen's heads jammed halfway through its descent, causing the executioner to improvise with a nearby sword. So horrifically successful was his resultant mime that three members of the audience fainted, an ordeal that continued for one punter when a St John ambulance man tried to revive her with a glass of tomato juice from the bar.

But perhaps the best example of the ways in which actors deal with alarums and excursions is from the 1996 NT's staging of Ibsen's John Gabriel Borkman (pictured). One ravishing visual moment, a gentle descent of snowflakes on to the main characters, had to be aborted when the snow machine broke down, and a tremulous stage manager was dispatched to break the news to the three principal actors: a Vanessa Redgrave, Eileen Atkins and the late, lamented Paul Scofield.

While Miss Redgravewas said to have responded in the best traditions of the Blitz by suggesting that tiny pieces of paper be torn up by stagehands secreted in the flies, Miss Atkins allegedly confined her reaction to a coruscating critique of stage machinery and its chronic unreliability in general. Eventually the stage manager reached Scofield's dressing room. the latter's four-word response was as poetic as it was damning. “No snow? No Sco...”

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