IC truck emissions should always be a concern for companies that run IC trucks indoors on a consistent basis. It is up to the customer to make sure they monitor the CO levels and keep their machines maintained to insure the CO levels are kept to an acceptable level. Proper building ventilation is also a factor.
As for as which brand lift has more CO emissions versus another? As i said previously, it all depends on the maintenance and the consistency of monitoring the trucks emissions and making sure they are tuned up and CO levels kept down to a minimum. Sure, if there is a real concern about CO emissions then install CO detectors to monitor this throughout the areas effected.