I volunteer on my University's 'Entertainments Crew' who handle the sound & light in the Students' Union for discos/bands/club nights etc. The first week of the new academic year (late September) always has special events where we get to spend a bit of cash hiring in equipment & effects we don't own.
We've hired scanning lasers before but always aimed them above the crowd as none of us had done enough research into the safety of aiming them at the crowd. Well this September I want to do some crowd scanning & as it was my idea I've been put in charge of determining the safety of such an effect, what scanners will be suitable, where we will be able to rig the scanners, etc.
I've read through HS(G)95 & the summary document published by Terralec & I'm starting to find out how restrictive the recommendations are. HS(G)95 doesn't contain any example distances for scanners, but the Terralec document gives the following table of 'hazard distances' (which I presume means that within that distance MPE is exceeded) for a scanner drawing a stationary circular tunnel (I doubt a moving tunnel will increase the distances that much), with a spread of 50 degrees, a scan rate of 20Hz & presuming a divergence of 2 mradians;
10mW : 5m
30mW : 9m
50mW : 11m
100mW : 16m
250mW : 26m
450mW : 35m
In addition to that, HS(G)95 recommends that you keep a 3m vertical distance between anywhere the audience can access (eg the dance floor) & any beams that exceed MPE.
I haven't heard back from the guy in charge with accurate dimensions of the venue, but from my guesstimates it's about 30 feet tall (about 9.1m). From the numbers provided by Terralec that means we'll struggle to use anything more than about 15-20mW for audience scanning.
Does this seem about right, or am I doing something wrong? Even if we only use green for audience scanning & keep the hazer on full all night, is the audience really going to see an impressive effect when 2x piddly 20mW scanners open up on them?
We've hired scanning lasers before but always aimed them above the crowd as none of us had done enough research into the safety of aiming them at the crowd. Well this September I want to do some crowd scanning & as it was my idea I've been put in charge of determining the safety of such an effect, what scanners will be suitable, where we will be able to rig the scanners, etc.
I've read through HS(G)95 & the summary document published by Terralec & I'm starting to find out how restrictive the recommendations are. HS(G)95 doesn't contain any example distances for scanners, but the Terralec document gives the following table of 'hazard distances' (which I presume means that within that distance MPE is exceeded) for a scanner drawing a stationary circular tunnel (I doubt a moving tunnel will increase the distances that much), with a spread of 50 degrees, a scan rate of 20Hz & presuming a divergence of 2 mradians;
10mW : 5m
30mW : 9m
50mW : 11m
100mW : 16m
250mW : 26m
450mW : 35m
In addition to that, HS(G)95 recommends that you keep a 3m vertical distance between anywhere the audience can access (eg the dance floor) & any beams that exceed MPE.
I haven't heard back from the guy in charge with accurate dimensions of the venue, but from my guesstimates it's about 30 feet tall (about 9.1m). From the numbers provided by Terralec that means we'll struggle to use anything more than about 15-20mW for audience scanning.
Does this seem about right, or am I doing something wrong? Even if we only use green for audience scanning & keep the hazer on full all night, is the audience really going to see an impressive effect when 2x piddly 20mW scanners open up on them?
