ROBERT STEFFEN: "At the hajj, it’s particularly senior adults who attend, and so they have great risk of suffering of heat stroke and of dying."

Stampedes and crushing at mass gatherings have caused an estimated seven thousand deaths over the past thirty years.

The design of an area can play a part. There may be narrow passages or other choke points that too many people try to use at once. Professor Steffen says the mood of a crowd can also play a part.

ROBERT STEFFEN: "If suddenly they get agitated, for instance, firework is being launched within a football stadium, then they get very much afraid and try to escape."

He says organizers of large gatherings need to avoid creating conditions that might lead to panic, stampedes and heat stroke. And he says they must be ready to give medical care.

So what advice does he have for people attending a large gathering? First, get any needed vaccinations before traveling. Then, stay away from any large mass of people as much as possible. Also, be careful with alcohol and drugs, which can increase the risk of injuries.

And that’s the VOA Special English Health Report, available online at voaspecialenglish.com with texts, MP3s, podcasts and captioned videos. Have you ever been in a huge crowd and worried about your safety? Or did you feel fine? Tell us about your experience. Post a comment at voaspecialenglish.com. I’m Christopher Cruise.