Anyone use heat plates?

[Tiff 36]

I received an order of day-old standard sized chicks in a variety of breeds in the mail Friday morning, they hatched Tuesday so are 5 days old now.  Everyone arrived healthy and were under lamps and eating/drinking since then, split into 4 large brooders in my breakfast room where i spend a lot of time watching them (they go down to the kennel in a week where they have more room and are out of my house).  Friday/Saturday I had a heat plate in one brooder (first time I've used one, they use a lot less power and are supposed to be safer than lamps) and this afternoon I moved the plate to a different brooder and moved the lamp to the first brooder just to move it around.  An hour later in the brooder with the plate one of the orpingtons was dead, no sign of stress or damage and she felt the same weight as the others, just dead?  It's been 6 hours and everyone else is fine, I "know" it wasn't the plate, but I'm just unsure.

 Just weird that it just up and died out of the blue?  I had 3 orders from the same hatchery last year with 350 chicks and other than one box that had Polish, houdans and apenzellar spitzbahabans that half were dead or failed to thrive, I've not had one that just up and died like that.  Thoughts?

[vfr400boy 3,120]

Iv used heat lamps and electric hens but prefer the lamps because you can always see them no hiding under the electric hen , sometimes you do get the odd one die