Lead and its compounds in detonator time delays are being phased out owing to environmental and health concerns. It was found that changing from the conventional rolled lead elements to rigid aluminium tubes caused a significant decrease in the burn rate. It also impaired ignitability, especially of slow burning compositions such as Si-BaSO4. Consequently, potential alternatives for the latter and also the fast burning Si-Pb3O4 system were sought. Bi2O3, prepared by thermal decomposition of bismuth subcarbonate, gave fast burning compositions with silicon as fuel (155 mm s(-1) with 20% Si). This system was ignitable by the spit of a shock tube. The Si-Sb6O13 system required an initiating composition and yielded slow burning compositions. The lowest sustainable and reproducible burn rate in lead tubes, in the absence of additives, was 4.8 mm s(-1). In lead tubes, it was possible to reduce the burn rate further by adding fumed silica: A composition obtained by adding 10% fumed silica (add-on basis) to a 10% Si-90% Sb6O13 composition still burned reliably at a burn rate of 2.3 mm s(-1).