MB 19: for the first paragraph - This implies that for the rest he may [continue working], and even for the Blessings of the Shema. This is clearly stated in Beis Yosef in Siman 66. Look later in the Taz in Siman 191:1 (who states clearly one may not do anything else whilst performing any Mitzvah). This [contradiction] presents a serious problem.
63:8. Employees or even the owner (*) who are working at the top of a tree or a building site, may read the Shema where they are and need not come down. [* One might have thought that the employees, who are bound to their work by contract, should not take the necessary time to come down, but the owner himself would have to descend. --YM]
63.9: A porter, even though his load is (20) on his shoulders may read the Shema, but he should not start [the Shema] while loading or unloading because his mind is not at ease.
MB 20: on his shoulders - Even if the load is 4 Kav [1 Kav is 1.38 Litres according to R. Avraham Noeh or 2.4 Liters according to the Chazon Ish] when in which case saying the Amidah would be forbidden, [as we will see] later in Siman 97:5. [However], with regard to the Shema it is permitted.
Jonathan Chody jonathan@quantime.co.uk